U.S. patent application number 11/718352 was filed with the patent office on 2009-08-13 for system and method for conserving oxygen delivery while maintaining saturation.
Invention is credited to James M. Davenport.
Application Number | 20090199855 11/718352 |
Document ID | / |
Family ID | 36319783 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090199855 |
Kind Code |
A1 |
Davenport; James M. |
August 13, 2009 |
SYSTEM AND METHOD FOR CONSERVING OXYGEN DELIVERY WHILE MAINTAINING
SATURATION
Abstract
A system and method, for maintaining a predetermined level of a
treatment gas in a patient while conserving use of the treatment
gas, comprising a source of the treatment gas, a sensing device for
sensing a breathing cycle of a patient, a conserver for controlling
intermittent supply of the treatment gas to the patient in response
to the sensed breathing cycle. In a first mode, when the sensing
device senses breathing, the treatment gas is intermittently
supplied to the patient at a supply rate coordinated with the
breathing cycle. In a second mode, when the sensing device is
unable to sense breathing, the treatment gas is supplied to the
patient at a second intermittent cycle, determined independently of
the patient breathing cycle, which is selected to overlap an
assumed patient breathing cycle such that at least a desired level
of the treatment gas is maintained in the patient.
Inventors: |
Davenport; James M.;
(Kingman, AZ) |
Correspondence
Address: |
DAVIS & BUJOLD, P.L.L.C.
112 PLEASANT STREET
CONCORD
NH
03301
US
|
Family ID: |
36319783 |
Appl. No.: |
11/718352 |
Filed: |
October 31, 2005 |
PCT Filed: |
October 31, 2005 |
PCT NO: |
PCT/US2005/039531 |
371 Date: |
January 14, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60624047 |
Nov 1, 2004 |
|
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|
Current U.S.
Class: |
128/204.23 |
Current CPC
Class: |
A61M 2202/03 20130101;
A61M 2205/18 20130101; A61M 16/0677 20140204; A61M 2205/8206
20130101; A61M 16/203 20140204; A61M 2202/0208 20130101; A61M
16/1015 20140204; A61M 16/202 20140204; A61M 2230/205 20130101;
A61M 2016/0021 20130101; A61M 2016/0027 20130101; A61M 16/205
20140204; A61M 16/024 20170801; A61M 2205/14 20130101; A61M 2205/70
20130101; A61M 2230/63 20130101; A61M 16/0051 20130101; A61M 16/101
20140204; A61M 16/204 20140204; A61M 2202/0208 20130101; A61M
2202/0007 20130101 |
Class at
Publication: |
128/204.23 |
International
Class: |
A61M 16/00 20060101
A61M016/00 |
Claims
1. A system for conserving supply of a treatment gas to a patient,
the system comprising: a source of the treatment gas; a sensing
device for sensing a breathing cycle of a patient; a conserver for
controlling intermittent supply of the treatment gas to the patient
in response to the sensed breathing cycle; wherein the conserver
operates in a first mode when the sensing device senses the
breathing cycle to supply the treatment gas to the patient in a
first intermittent cycle coordinated with the breathing cycle; and
the conservator operates in a second mode, when the sensing device
is unable to sense the breathing cycle, in which the conserver
supplies the treatment gas to the patient at a second intermittent
cycle determined independently of the patient breathing cycle where
the second intermittent cycle is selected to overlap an assumed
patient breathing cycle such that at least a desired amount of the
treatment gas is supplied to the patient.
2. The system according to claim 1, wherein during operation of the
system in the second mode, the system has a treatment gas delivery
period that is less than a duration of an interruption period.
3. The system according to claim 1, wherein during operation of the
system in the second mode, the system delivers treatment gas to the
patient at a rate ranging from ten to forty gas delivery periods
per minute.
4. The system according to claim 3, wherein during operation of the
system in the second mode, the system delivers treatment gas to the
patient at a rate of twenty treatment gas delivery periods per
minute.
5. The system according to claim 1, wherein during operation of the
system in the second mode, the system delivers treatment gas to the
patient a rate sufficient to maintain saturation of the
patient.
6. The system according to claim 1, wherein the source of a
treatment gas is one of a liquid oxygen source, a gaseous oxygen
source and a concentrator for removing nitrogen from air and
increasing a concentration of oxygen of the room air supplied as
the treatment gas.
7. The system according to claim 1, wherein the conserver is
coupled to a patient respiratory system interface which supplies
the treatment gas to the patient.
8. The system according to claim 7, wherein the patient interface
is a cannula with a first and second nares located for positioning
within the nostrils of the patient for delivery of the treatment
gas and for sensing a breathing cycle of the patient.
9. The system according to claim 8, wherein the cannula is a
divided cannula and the first nare communicates with the conserver
for delivering the treatment gas to one of the nostrils of the
patient and the second nare communicates with the sensing device
for sensing a pressure in the other nostril of the patient.
10. The system according to claim 1, wherein the sensing device is
one of a transducer and a pneumatic diaphragm.
11. The system according to claim 1, wherein the conserver includes
a concentrator for removing nitrogen from air and increasing a
concentration of oxygen of the room air supplied as the treatment
gas.
12. The system according to claim 3, wherein the conserver includes
a patient activity sensing device for indicating an activity level
of the patient and the patient activity sensing device facilitates
adjustment of a duration of the treatment gas delivery period to
the patient according to a sensed activity level of the
patient.
13. The system according to claim 12, wherein the conserver, in
response to a predetermined sensed activity level of the patient,
adjusts the treatment gas delivery period such that the treatment
gas is delivered to the patient only during every other treatment
gas delivery period.
14. The system according to claim 1, wherein the conserver, in
response to at least one of a power supply failure and a system
component failure, operates a bypass valve connected between the
treatment gas source and the patient interface to enter the open
state to allow a continuous flow of the treatment gas to the
patient interface.
15. The system according to claim 14, wherein the conserver further
includes a regulator connected in line with the gas source and the
bypass valve to control at least one of a flow rate and a pressure
of the treatment gas to the patient interface.
16. The system according to claim 14, wherein upon cessation of
power to the bypass valve, the bypass valve automatically enters an
open state.
17. A system for maintaining a predetermined level of a treatment
gas in a patient while conserving use of the treatment gas, the
system comprising: a source of oxygen; a sensing device for sensing
a breathing cycle of a patient; a conserver for controlling
intermittent supply of the oxygen to the patient in response to the
sensed breathing cycle; wherein the conserver operates in a first
mode when the sensing device senses the breathing cycle to supply
the oxygen to the patient in a first intermittent cycle coordinated
with the breathing cycle immediately prior to the patient
commencing inhalation so that the supplied oxygen dilutes and
diffuses any carbon dioxide contained in the exhaled breath of the
patient while also enriching a concentration of oxygen available
for inhalation by the patient during a next inhalation breath; the
conservator operates in a second mode, when the sensing device is
unable to sense the breathing cycle, in which the conserver
supplies the oxygen to the patient at a second intermittent cycle
determined independently of the patient breathing cycle; the second
intermittent cycle is selected to overlap an assumed patient
breathing cycle such that at least a desired amount of the
treatment gas is supplied to the patient; and the conserver, in
responsive to at least one of a power supply failure and a system
component failure, is actuated to an open state to allow a
continuous flow of the oxygen to the patient interface.
18. The system according to claim 17, wherein the conserver
includes a patient activity sensing device for sending an activity
level of the patient and the patient activity sensing device
facilitates adjustment of a duration of an oxygen delivery period
to the patient according to the sensed activity level of the
patient; and the conserver, in response to a predetermined sensed
activity level of the patient, adjusts the oxygen delivery period
such that the oxygen is delivered to the patient only during every
other oxygen delivery period.
19. A method for maintaining a predetermined level of a treatment
gas in a patient while conserving use of the treatment gas by
delivering the treatment gas from a treatment gas source and to a
patient interface via a conserver connected between the treatment
gas source and the patient interface, the method comprising the
steps of: sensing parameters of a breathing cycle of the patient;
controlling operation of the conserver according to the sensed
parameters of the breathing cycle so that the conserver operates in
one of a first mode and a second mode; during the first mode, when
at least one parameter of the breathing cycle is sensed, the
conserver supplying the treatment gas to the patient in a first
intermittent cycle coordinated with the patient breathing cycle,
and during the second mode, when the conserver is unable to sense
at least one parameter of the breathing cycle, the conserver
supplying the treatment gas to the patient in a second intermittent
cycle determined independently of the patient breathing cycle, in
which the second intermittent cycle is selected to overlap an
assumed patient breathing cycle such that at least a desired level
of the treatment gas is maintained in the patient.
20. The method according to claim 19, further comprising the step
of, during the second mode of operation, using a treatment gas
delivery period that is approximately one half a duration of a gas
interruption period.
21. The method according to claim 19, further comprising the step
of, during the second mode of operation, delivering the treatment
gas at a rate ranging from ten to forty treatment gas delivery
periods per minute.
22. The method according to claim 21, further comprising the step
of, during the second mode of operation, delivering the treatment
gas at a rate of approximately twenty treatment gas delivery
periods per minute.
23. The method according to claim 21, further comprising the step
of, during the second mode of operation, delivering the treatment
gas at a rate sufficient to maintain saturation of the patient with
the treatment gas.
24. The method according to claim 19, further comprising the step
of using one of a liquid oxygen source, a gaseous oxygen source and
a concentrator as the source of the treatment gas.
25. The method according to claim 19, further comprising the step
of using a divided cannula and communicating a first nare with the
conserver for delivering the treatment gas to one of the nostrils
of the patient and communicating a second nare with the sensing
device for sensing pressure in the other nostril of the
patient.
26. The method according to claim 19, further comprising the step
of using one of a transducer and a pneumatic diaphragm as the
sensing device.
27. The method according to claim 19, further comprising the step
of providing the conserver with a concentrator for removing
nitrogen from air and increasing a concentration of oxygen to be
supplied as the treatment gas.
28. The method according to claim 19, further comprising the step
of providing the conserver with a patient activity sensing device
for sensing an activity level of the patient and the patient
activity sensing device facilitates adjustment of a duration of the
treatment gas delivery period to the patient according to a sensed
activity level of the patient.
29. The method according to claim 28, further comprising the step
of the conserver, in response to a predetermined sensed activity
level of the patient, adjusting the treatment gas delivery period
such that the treatment gas is delivered to the patient only during
every other treatment gas delivery period.
30. The method according to claim 19, further including the steps
of: detecting one of a power supply failure and a system component
failure, and actuating a bypass valve, connected between the
treatment gas source and the patient interface, to an open state
and allow a continuous flow of the treatment gas to the patient
interface.
31. The method according to claim 30 further including the step of
determining the flow of treatment gas to the patient interface by a
regulator connected in line with the gas source and the bypass
valve.
32. The method according to claim 30 further including the step of
the bypass valve automatically being actuated to the open state
upon cessation of power to the bypass valve.
33. A system for conserving supply of a treatment gas to a patient,
the system comprising: a source of the treatment gas; a sensing
device for sensing a breathing cycle of a patient; a conserver for
controlling intermittent supply of the treatment gas to the patient
in response to the sensed breathing cycle; wherein the conserver
supplies the treatment gas to the patient at an intermittent cycle
determined independently of the patient breathing cycle where the
intermittent cycle is selected to overlap an assumed patient
breathing cycle such that at least a desired amount of the
treatment gas is supplied to the patient.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present patent application is related to U.S. Pat. No.
5,697,364 issued on Dec. 16, 1997 to Chua et al. for an
INTERMITTENT GAS-INSUFFLATION APPARATUS.
FIELD OF THE INVENTION
[0002] The present invention relates to a system and method for
insufflating a quantity of a gaseous treatment fluid, which may be,
for example, a gas such as oxygen or some other gas, a mixture of
gases, including air enriched with additional oxygen or depleted of
nitrogen to increase the proportion of oxygen therein, a gas or gas
mixture carrying dispersed liquid droplets or solid particles, into
an entrance of a respiratory system of a breathing patient to
maintain a desired saturation level of the treatment gas in the
patient while conserving consumption of the treatment gas, but
maintaining an acceptable level of treatment gas in the patient
under fault conditions, such as a loss of inhalation/exhalation
data from the patient or a loss of power in the system.
BACKGROUND OF THE INVENTION
[0003] Systems for the controlled delivery of a treatment gas which
may be, for example, a gas such as oxygen or some other gas, a
mixture of gases, including air enriched with additional oxygen or
depleted of nitrogen to increase the proportion of oxygen therein,
a gas or gas mixture carrying dispersed liquid droplets or solid
particles, are well known in the prior art and typically comprise a
gas source, a gas regulator and a gas conserver which cooperate to
deliver the treatment gas from the source to the patient in a
controlled manner. For example, in a typical treatment gas delivery
system 1P, as diagrammatically illustrated in FIG. 1, the treatment
gas such as oxygen or any gas or gas/particulate/droplet mixture,
is generally contained in and provided from a gas source 2P which
may be, for example, a gas tank containing a treatment gas such as
gaseous or liquid oxygen or gas concentrator delivering the
treatment gas, and is supplied through a supply conduit 4P to a
regulating device, which is typically of the type of regulator
referred to as a conserver 6P. The conserver 6P will then output a
desired quantity of the treatment gas through a patient conduit 8P
at a desired pressure and flow rate, typically, at a flow rate of
from 1 to 6 liters per minute, for example. In a typical system the
treatment gas, such as oxygen, is typically delivered to the
patient by a cannula or some other face piece worn by the patient
which feeds the oxygen into the nasal cavities or possibly the
mouth cavity of the patient. From there, the delivered oxygen is
inhaled by the patient into the lungs for absorption into the blood
stream of the patient.
[0004] As indicated, the conserver 6P typically includes pressure
sensing equipment 10P associated with the patient 12P to detect the
breathing cycles of the patient. That is, each breathing cycle
includes an inhalation interval and an exhalation interval, also
respectively referred to as a negative pressure interval and a
positive pressure interval, and, in general, the sensing equipment
10P will determine when the patient is commencing an inhalation, or
negative pressure, interval and will then supply the treatment gas
to the patient for the duration of time during which the patient is
inhaling. When the sensing equipment 10P determines that the
patient's inhalation interval has ceased, the conserver 6P will
discontinue the supply of treatment gas to the patient 12P until
the sensing equipment 10P again senses that the patient 12P is
commencing another inhalation interval, at which time the supply of
treatment gas to the patient 12P is again commenced. By
intermittently interrupting the delivery of oxygen to the patient,
the quantity of treatment gas delivered to the patient is
conserved, e.g., reduced or minimized, without seriously impacting
the saturation level of the patient 12P.
[0005] It must be noted that the gas source 2P may typically
comprise either a tank or some other storage structure, such as for
gaseous or liquified oxygen, or of a treatment gas generator, such
as a conventional concentrator. In the case of a concentrator,
which is typically employed when the treatment gas is oxygen or
oxygen enriched air, for example, the concentrator employs
molecular sieves to absorb some of the nitrogen from the room air,
thereby providing a treatment gas to the conserver 6P having a
proportionally increased oxygen content.
[0006] There are a number of drawbacks associated with the
treatment gas systems of the prior art, one of which is that the
systems of the prior art typically dispense the treatment gas, such
as oxygen, only when the system senses the beginning of an
inhalation interval by a patient. One of the problems associated
with this technique is that there is a time delay from the time
when an inhalation interval is detected and the conserver is
actuated to the time that the oxygen is actually delivered to the
patient. As a result of this delay, the initial volume of air
inhaled by the patient primarily comprises the partially exhaled
breath of the patient as well as the unconcentrated room air which
does not contain an elevated or increased amount of oxygen therein.
As a result of this, the air initially inhaled by the patient does
not have an elevated or increase level of oxygen therein.
[0007] This problem is more serious than first appears, however,
and the full complexity of the problems associated with the gas
dispensing systems of the prior art can be fully understood only
when the actual nature of a patient breathing cycle is considered
and understood in detail. First considering the breathing cycle
itself, a plot of the breathing pressure of the patient as a
function of time over the breathing cycle, the pressures occurring
in a breathing cycle generally appear as a modified sine wave. That
is, during the exhalation interval there is a positive breathing
pressure having a form generally corresponding to one half of a
sine wave form as the pressure rises then falls relative to ambient
air pressure. Correspondingly, during the inhalation interval,
there is a negative breathing pressure having a form generally
corresponding to the second half of a sine wave form as the
pressure continues to fall after termination of the exhalation
interval and then rises relative to the ambient air pressure. In
actuality, the sine wave form of the breathing cycle is skewed so
that the exhalation interval of the skewed sine wave constitutes,
on an average, about two thirds of the breathing cycle while the
inhalation interval of the skewed sine wave constitutes, on an
average, about one third of the breathing cycle.
[0008] Furthermore, the respiratory system of the patient includes
the passageway to the lungs comprising the nares of the nose, the
nasal cavity and the trachea which together provide a conduit for
transporting ambient atmospheric air to and fro a person's lungs.
This passageway is anatomically dead space that, after the
exhalation interval, is now filled with exhaled air which, in turn,
becomes the first initial quantity of inhaled air during the
subsequent inhalation interval. By way of example only, on the
average, this anatomically dead space retains about the first one
third (1/3) of the quantity of air for the next inhalation. The
remaining two thirds (2/3) of the quantity of air required for
breathing is provided by fresh ambient atmospheric air during the
subsequent inhalation interval. However, only about one half (1/2)
of this fresh ambient air actually reaches the lungs for gaseous
exchange, i.e., only about the second one third (1/3) of the
required air (or the first one half (1/2) of the fresh air) is
carried to the lungs while the last one third (1/3) of the required
air (or the second one half (1/2) of the fresh air) never actually
reaches the lungs and remains in the anatomically dead space.
Therefore, on the average, only 16% to 17% of the breathing cycle
brings fresh air or fresh air combined with the insufflation gas to
the lungs and this occurs only during the first one half (1/2) of
the inhalation interval of the breathing cycle.
[0009] As a consequence of the two factors discussed above, it is
apparent that only the gas delivered during a relatively small part
of the breathing cycle actually reaches the patient's lungs to be
of benefit to the patient, and continuous flow systems are
obviously very inefficient in terms of the consumption and use of
the treatment gas.
[0010] In response to this problem, many systems and devices of the
prior art have included oxygen-conserving features, which are
generally characterized as either "on demand" systems or "on the
go" systems. In general, "on demand" means that oxygen is not
delivered to the patient until after the beginning of the
inhalation interval of the breathing cycle and that no oxygen is
delivered to the patient during any portion of the exhalation
interval of the breathing cycle. Since oxygen was not delivered to
the patient during the exhalation interval, which constitutes two
thirds of the entire breathing cycle, significant quantities of
oxygen were conserved.
[0011] Examples of "on demand" systems include U.S. Pat. No.
4,462,398 and U.S. Pat. No. 4,519,387 to Durkan et al. wherein a
control circuit, responsive to a sensor, operates a valve to supply
pulses of respirating gas through a single hose cannula to a
respiratory system of a patient when a negative pressure,
indicative of the initial stage of inhalation or inspiration, is
sensed by the sensor. The pulse of gas delivered to the respiratory
system can have a preselected pulse profile. This method provides
for supplying a fixed volume of supplemental respiratory gas per
unit of time. The volumetric flow rate of the supplemental
respiratory gas is preset and the time duration of each application
of the supplemental respiratory gas is also preselected, thereby
providing a fixed volume of respiratory gas after the beginning of
inhalation. Also, this method provides for a minimal delay interval
between successive applications of respiratory gas and such delay
interval is also predetermined since the time interval for
respiratory gas flow is preset for a time less than the time of the
inspiration.
[0012] Another prior art supplemental oxygen delivery system
designed to conserve respiratory gas by delivering oxygen "on
demand" only during inhalation is described in U.S. Pat. No.
4,612,928 to Tiep et al. which discloses both a method and
apparatus for supplying a gas to a body. The apparatus and method
are employed to minimize the amount of oxygen needed to maintain a
specific oxygen concentration level in the blood of an individual.
The apparatus includes a transducer and other circuit components to
obtain a first series of pulses or signals corresponding to the
individual's breath rate. A divider or counter processes the
signals or pulses of the first series to create a second series of
pulses or signals corresponding to periodic pulses or signals of
the first series. The pulses or signals of the second series are
used to periodically open a valve to deliver oxygen to the
individual at about the start of the inhalation interval of the
individual's periodic breathing cycles.
[0013] In further examples, such as U.S. Pat. Nos. 4,457,303 and
4,484,578, recognize that oxygen delivered at the end of the
inhalation interval of the breathing cycle is wasteful. These two
patents describe respirator apparatuses and methods therefor. In
brief, a fluidically-operated respirator comprises an apneic event
circuit and a demand gas circuit. The apneic event circuit
comprises a variable capacitance device and an exhaust means which
rapidly discharges fluid from the circuit when inhalation occurs.
The demand gas circuit of the respirator supplies the respirating
gas to a patient at the beginning of inhalation and for a time
period which is a fraction of the duration of the inhalation. Thus,
these patents also follow the reasoning that insufflation at the
beginning of inhalation will effectively supply the respirating gas
to the patient.
[0014] In yet another prior art system, a supplemental oxygen
delivery system begins to deliver a steady flow of oxygen during a
later stage of the exhalation interval and through an advanced
stage of the inhalation interval of the breathing cycle and
superimposes upon this steady flow of oxygen a peak pulse flow of
oxygen at the beginning of inhalation. This is described in U.S.
Pat. No. 4,686,974 to Sato et al. which discloses a
breath-synchronized gas-insufflation device. This device includes a
gas source, a valve, an insufflating device, a sensor, and an
operational controller. The valve is connected to the gas source so
as to regulate flow rate and duration of the gas flow from the gas
source. The insufflating device is connected to the valve so as to
insufflate the gas therefrom toward a respiratory system of a
living body. The sensor is exposed to respiration of the living
body and produces electric signals which must distinctively
indicate an inhalation interval and an exhalation interval of the
breathing cycle. The operational controller receives the electric
signals from the sensor and produces control signals to the valve
so that gas insufflation starts before the beginning of the
inhalation interval and ends before termination of the inhalation
interval while providing a short pulse-like peak flow of a large
amount of the gas in an early stage of the inspiratory interval.
Specifically, steady insufflation of the gas starts before the
beginning of each inhalation and the pulse-like peak flow
insufflation of the gas is superimposed on the steady insufflation
for a short period of time after the beginning of the inhalation.
An arbitrary time interval, based upon an average exhalation period
and an average inhalation period, is chosen to trigger and end
insufflation during the breathing cycle.
[0015] Although the prior art devices discussed hereinabove indeed
conserve a treatment gas, such as oxygen, they fail to address the
problem related to the changing respiratory needs of the patient
that vary with different patient activity levels. When a patient
requiring supplemental oxygen is at rest, relatively small
quantities of oxygen are needed to maintain appropriate levels of
oxygen concentration in the blood and thereby prevent what is
termed "desaturation". With an increase in the physical activity of
a patient, larger quantities of oxygen are needed to maintain
appropriate levels of oxygen concentration in the blood compared to
when the patient is at rest.
[0016] Such systems are generally referred to as "on the go"
systems and an example of such is U.S. Pat. No. 4,706,664 wherein
Snook et al. discloses a pulse-flow supplemental oxygen apparatus
which yields savings in oxygen while affording the patient the
physiological equivalent of a prescribed continuous stream of
oxygen. The apparatus includes a demand oxygen valve operated in a
pulse mode by means of electronic control circuitry. Through an
appropriate sensor, the electronic control circuitry monitors the
patient's breathing efforts and gives a variable timed pulse of
oxygen to increase the volume delivered to the patient during the
very initial stage of each inhalation interval of the breathing
cycle or breath. Pulse volume variability is based upon a measured
parameter characterizing a plurality of the patient's preceding
breathing cycles. The elapsed time interval of the patient's three
preceding breathing cycles is measured to effectively measure the
rate of the breathing cycles. These breath-characterizing
parameters, together with data characterizing the prescribed
continuous oxygen flow to be matched, enable the apparatus to give
the desired dose variability.
[0017] In yet another example, U.S. Pat. No. 4,584,996 to Blum
reveals a method and apparatus for intermittent administration of
supplemental oxygen to patients with chronic lung dysfunction. The
apparatus is programmable for administering the specific oxygen
requirements of the patient and is responsive to changes in these
oxygen requirements with increased patient activity. The patient's
arterial blood oxygen level is measured while supplying oxygen to
the patient during inspiration to determine the number of breathing
cycles required to reach a first higher arterial blood oxygen level
and is again measured without supplemental oxygen to determine the
number of breathing cycles required to diminish the arterial blood
oxygen level to a second, lower level. These two cycle numbers are
utilized in an algorithm which is applied as a program to the
apparatus having a breathing cycle sensor, a counter and control
valve. The control valve provides a regulated flow of supplemental
oxygen to a nasal cannula for a predetermined number of "ON"
breathing cycles and to shut off the flow for a preset number of
"OFF" breathing cycles sequentially and repetitively, thereby
conserving oxygen while medically monitoring the patient's blood
oxygen levels. The oxygen conservation features of this apparatus
are further enhanced by turning off the oxygen flow during the
exhalation interval of each breathing cycle throughout the "ON"
breathing cycles. As the respiratory rate of the patient increases
with patient activity, the duration of the "ON" and "OFF" periods
changes accordingly.
[0018] In U.S. Pat. No. 4,686,975, Naimon et al. teaches a
supplemental respiratory device that uses electronic components to
intermittently regulate the flow of a respirable gas to a user on a
demand basis. By monitoring small changes in the relative airway
pressure, this respiratory device supplies gas only when an
inhalation is detected. This respiratory device can also vary the
duration of the gas delivery time to compensate for changes in the
user's breath rate, thereby attempting to adjust for changes in the
patient's respiratory needs based upon activity.
[0019] There are many other examples of "on demand" and "on the go"
systems as many manufacturers are marketing oxygen conserver
devices which are adapted to retrofit onto typical supplemental
oxygen delivery systems that employ any type of oxygen source, such
as portable oxygen tanks, oxygen concentrators or wall outlet
supplies often utilized in hospitals. These oxygen conserver
devices are adapted to be interposed between the oxygen source and
a conventional nasal cannula apparatus. Medisonic U.S.A., Inc. of
Clarence, N.Y., manufactures an oxygen conserver device entitled
MedisO.sub.2 nic Conserver. It conserves oxygen by interrupting the
flow of oxygen from the source to the patient during the exhalation
interval of the patient's breathing cycle. Chad Therapeutics, Inc.
of Chatsworth, Calif., manufacturers an oxygen conserver device
bearing a registered trademark, Oxymatic.RTM. Electronic Oxygen
Conserver. Chad's oxygen conserver eliminates oxygen waste during
both the exhalation interval and the later portion of the
inhalation interval of the breathing cycle. TriTec, Inc. of
Columbia, Md., manufactures a demand oxygen cannula for portable
oxygen systems that also responds to the negative pressure of
inhalation. Smith-Perry Corporation of Surrey, British Columbia,
Canada, manufactures The VIC (Voyager Intermittent Controller)
Breathsaver that senses every breath of the patient and delivers a
measured dose of oxygen only when the patient inhales. Pulsair,
Inc. of Fort Pierce, Fla., manufactures an oxygen management system
that delivers oxygen to the patient "on demand" at the initiation
of inhalation. The Henry G. Dietz Co., Inc. of Long Island City,
N.Y., manufactures an oxygen conserver device entitled Hala'tus 1
which conserves oxygen by sensing when inhalation takes places and
delivers the oxygen only during inhalation.
[0020] It must be noted, however, that none of these oxygen
conserver devices deliver oxygen to the patient during any stage of
exhalation, and thus do not operate in accordance with the actual
characteristics of the breathing cycle and the patient breathing
system. In addition, none of these systems address the problems
associated with maintaining an acceptable level of treatment gas in
the patient under fault conditions, such as a loss of
inhalation/exhalation data from the patient or a loss of power in
the system.
SUMMARY OF THE INVENTION
[0021] Wherefore, it is an object of the present invention to
overcome the above noted drawbacks associated with the prior art
treatment gas delivery systems.
[0022] Another object of the present invention is to provided a
system and method which commences delivery of a treating gas, such
as oxygen or room air with a concentrated or increased level of
oxygen, to a patient during the final stage of the exhalation
breath of the patient so that air, e.g., oxygen or room air with a
concentrated or increased level of oxygen, is instantaneously
available, at the nasal and/or mouth cavities of the patient,
immediately prior to the time when the patient commences an
inhalation breath. As a result of this, oxygen or room air with a
concentrated or increased level of oxygen, is instantaneously
available for inhalation at the beginning of the inhalation breath
of the patient.
[0023] A further object of the present invention is to supply a
bolus or pulse of a treating gas such as oxygen or room air with a
concentrated or increased level of oxygen, directly to the nasal
cavities and/or mouth cavity of the patient, immediately prior to
the patient commencing an inhalation breath, so that this bolus or
pulse of concentrated or increased level of oxygen is able to
dilute the carbon dioxide concentration and increase the oxygen
concentration of the air or gases contained within the nasal
cavities and/or mouth cavity of the patient prior to the patient
commencing his/her inhalation breath. This initial pulse or bolus
of oxygen is effective in diluting the concentration of carbon
dioxide contained within the nasal cavities, the mouth cavity, the
larynx and/or the bronchi of the patient and also enriches or
increases the oxygen concentration of the gases contained in those
areas immediately prior to the patient commencing his/her
inhalation breath. Such dilution of the concentration of carbon
dioxide and enrichment of the concentration of oxygen will, in
turn, assist in maintaining the blood oxygen saturation level of a
patient at approximately 92% to 93%.
[0024] Yet another object of the present invention is to provide a
failure mechanism which is designed to provide an adequate supply
of oxygen, e.g., room air with a concentrated or increased level of
oxygen, to the patient in the event that the system or method is
unable to detect, determine or sense breathing of the patient. The
failure mechanism ensures that the treatment gas saturation level
or the blood oxygen saturation level of the patient remains
adequately saturated with oxygen, e.g., at a blood saturation
oxygen level of approximately 92% to 93% during use of the
system.
[0025] A still further object of the present invention is to
provide a system and method which delivers treating gas such as
oxygen at a rate of 20 cycles per minute, or some other desired
delivery rate, in the event the system and method fail to detect,
determine or sense breathing of a patient. For example, the system
or method will deliver oxygen to the patient for an interval of
about 1 second or so and then interrupt the flow of oxygen to the
patient for an interval of about 2 seconds or so, and then again
deliver oxygen to the patient for a further interval of about 1
second or so and then interrupt the flow of oxygen to the patient
flow for an interval of about 2 seconds or so, and so forth,
thereby providing 20 oxygen delivery cycles per minute to the
patient.
[0026] Yet another object of the present invention is to provide
the system and method with a default mode of operation so that, in
the event that a malfunction of the power source or some other
component of the conserver, the oxygen control valve is controlled
to its normally open default state to supply a continuous flow of
oxygen, of some other treating gas to the patient, and ensure that
the patient receives a continuous and constant supply of oxygen or
some other treating gas and is maintained adequately saturated even
during malfunction of one or more components of the system or
method.
[0027] The present invention also relates to a system for
conserving supply of a treatment gas to a patient, the system
comprising: a source of the treatment gas; a sensing device for
sensing a breathing cycle of a patient; a conserver for controlling
intermittent supply of the treatment gas to the patient in response
to the sensed breathing cycle; wherein the conserver operates in a
first mode when the sensing device senses the breathing cycle to
supply the treatment gas to the patient in a first intermittent
cycle coordinated with the breathing cycle; and the conservator
operates in a second mode, when the sensing device is unable to
sense the breathing cycle, in which the conserver supplies the
treatment gas to the patient at a second intermittent cycle
determined independently of the patient breathing cycle where the
second intermittent cycle is selected to overlap an assumed patient
breathing cycle such that at least a desired amount of the
treatment gas is supplied to the patient.
[0028] The present invention also relates to a method for
maintaining a predetermined level of a treatment gas in a patient
while conserving use of the treatment gas by delivering the
treatment gas from a treatment gas source and to a patient
interface via a conserver connected between the treatment gas
source and the patient interface, the method comprising the steps
of: sensing parameters of a breathing cycle of the patient;
controlling operation of the conserver according to the sensed
parameters of the breathing cycle so that the conserver operates in
one of a first mode and a second mode; during the first mode, when
at least one parameter of the breathing cycle is sensed, the
conserver supplying the treatment gas to the patient in a first
intermittent cycle coordinated with the patient breathing cycle,
and during the second mode, when the conserver is unable to sense
at least one parameter of the breathing cycle, the conserver
supplying the treatment gas to the patient in a second intermittent
cycle determined independently of the patient breathing cycle, in
which the second intermittent cycle is selected to overlap an
assumed patient breathing cycle such that at least a desired level
of the treatment gas is maintained in the patient.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The invention will now be described, by way of example, with
reference to the accompanying drawings in which:
[0030] FIG. 1 is a diagrammatic representation of a conventional
treatment gas apparatus of the prior art;
[0031] FIG. 2 is a schematic diagram of a first exemplary
embodiment of an intermittent gas-insufflation apparatus of the
present invention shown operably connected to and between a
breathing patient and a source of treatment gas;
[0032] FIG. 3 is a graph illustrating a flow rate profile of the
treatment gas being delivered to the patient superimposed over an
inhalation interval and an exhalation interval of an immediate
breathing cycle and a subsequent inhalation interval of a
successive breathing cycle;
[0033] FIG. 4 is a schematic diagram of a power source accompanied
by an electrical schematic diagram which is incorporated into the
intermittent gas-insufflation apparatus of the present
invention;
[0034] FIGS. 5A and 5B are schematic diagrams of a sensor, a
reference voltage generator, a controller in a form of a
microprocessor and a valve assembly including a first solenoid
valve and a second solenoid valve which are incorporated into the
intermittent gas-insufflation apparatus of the present
invention;
[0035] FIGS. 6A and 6B are flow diagrams of the software program
which shows the controller of the intermittent gas-insufflation
apparatus of the present invention;
[0036] FIG. 7 is a flow chart for a "failsafe" mechanism to ensure
an adequate level of treatment gas to the patent; and
[0037] FIG. 8 is a diagrammatic illustration of the operation of
the present invention for providing an acceptable level of
treatment gas to the patient under fault conditions, such as a loss
of inhalation/exhalation data from the patient or a loss of power
in the system.
DETAILED DESCRIPTION OF THE INVENTION
[0038] The present invention is directed at maximizing conservation
of the delivery of a treatment gas to a patient while, at the same
time, maintaining the patient adequately saturated during, for
example, a loss of respiratory data from the patient or a loss of
power in the system. Systems for doing so are frequently referred
to as "intermittent gas-insufflation" systems wherein the term
"gas-insufflation" refers generally to the delivery of a treatment
gas, such as oxygen or a carrier gas carrying suspended particles
or droplets of medication of some other treatment fluid(s) or
material(s), to a patient to be breathed in by the patient. The
term "intermittent", in turn, refers to such systems that do not
deliver a continuous flow of treatment gas, but instead deliver the
treatment gas only during those phases of the breathing cycle or
during those demand periods when the delivery would be
advantageous, thereby reducing the consumption of the treatment gas
while providing adequate levels of the treatment gas to a
patient.
[0039] The treatment gas may be, for example, oxygen, room air
having an elevated or increased concentration of oxygen, (e.g., a
diluted concentration of nitrogen) nitrous oxide, or any form of
gas having droplets or particles of a medication or some other drug
in suspension, and so on, all of which are herein after referred to
herein generically as a "treatment gas". It should be noted,
however, that the following discussions will often refer to the
treatment gas as "oxygen" or concentrated "room air", and it must
be understood that oxygen is selected for the following exemplary
embodiments because oxygen is one of the more common treatment
gases administered to a patient.
[0040] Therefore, for purposes of the following discussions and in
the case of oxygen or room air having an elevated or increased
concentration of oxygen as the treatment gas, the treatment gas is
supplied to maintain the blood oxygen saturation level of a patient
at approximately 92% to 93%. The inventor has determined that by
commencing delivery of oxygen or room air with an increased
concentration of oxygen as the treatment gas to the patient,
slightly or immediately prior to the patient completing his/her
exhalation breath, i.e., during the last 10% or so of the patient's
exhalation breath, this ensures that an adequate supply of oxygen
is delivered to and available for inhalation by the patient
immediately prior to the moment when the patient commences
inhalation. That is, immediately prior to the moment when the
patient commences inhalation, the oxygen or room air with an
increased concentration of oxygen is supplied to and fills the
nasal cavities and/or the mouth cavity of the patient for
inhalation by the patient.
[0041] In addition, the present invention is directed at supplying
the oxygen to those cavities or regions of the patient, immediately
prior to the patient commencing inhalation, so that the oxygen,
which is delivered by the conserver to the patient at a desired
pressure and flow rate, adequately dilutes and diffuses the
concentration of carbon dioxide contained in the exhaled breath of
the patient while, at the same time, enriches the concentration of
oxygen available for inhalation by the patient during his/her next
breath.
[0042] In this regard, room air ordinarily has an oxygen content of
about 22% while the gas being exhausted or exhaled from the lungs
of a patient typically has an oxygen content of about 17 to 18%,
for example. In particular, the exhaled gases from the lungs which
have not been completely exhaled from and are still located within
the trachea, the bronchi, the nasal cavities and/or the mouth
cavity of the patient typically have an oxygen content of 17 to
18%. As these gases have not been completely exhaled, these same
gases are the first gases that are initially inhaled by the patient
during the next subsequent breath.
[0043] The conserver and method of the present invention are
specifically directed at supplying an initial pulse or bolus (e.g.,
approximately 35 cc) of oxygen or room air with an increased
concentration of oxygen which is specifically designed to diffuse
the concentration of carbon dioxide and other gases contained
within breathing cavities and/or areas and enrich the concentration
of oxygen to about 20% to 21% or so, for example, depending upon
the flow rate of the oxygen, the supply pressure of the oxygen,
etc.
[0044] The inventor has, therefore, appreciated that during the
transition from exhalation to inhalation, the patient will
generally initially inhale the last portion of breath (e.g.,
approximately 150 cc or so depending upon the physical
characteristics of the patient) that was in the process of being
exhaled by the patient but was not expelled from the lungs, the
trachea, the nasal and/or mouth cavities. Accordingly, the present
invention is directed at diluting the concentration of the carbon
dioxide and increasing the concentration of oxygen contained in the
exhaled but not expelled breath of the patient so that, upon
commencing inhalation by the patient, the concentration of carbon
dioxide and oxygen initially inhaled by the patient during the
first 10% of the inhalation breath are optimized. At assist with
this, the conserver controls a flow valve which, when open,
releases the treatment gas which accumulates in a bolus chamber
(e.g., a 35 cc bolus chamber) and supplies this treatment gas
directly to the nasal and/or mouth cavities. This bolus or initial
pulse of oxygen is designed to dilute and diffuse the concentration
of carbon dioxide while, at the same time, enrich the concentration
of oxygen prior to the patient inhaling the next subsequent
breath.
[0045] First considering an exemplary intermittent gas-insufflation
apparatus in which the present invention can be and is implemented,
such a system is adapted to be disposed between and in fluid
communication with a source of gaseous treatment fluid, such oxygen
or air with an enriched oxygen content, and a breathing patient.
The intermittent gas-insufflation apparatus is operative to
insufflate a quantity of the treatment gas, e.g., oxygen, into an
entrance of a respiratory system of the patient after an inhalation
interval and during an exhalation interval of an immediate
breathing cycle and into a subsequent inhalation interval of a
successive breathing cycle of the patient. For purposes of
explaining the intermittent gas-insufflation apparatus of the
present invention, it would be beneficial to discuss several terms
used throughout the description of the exemplary embodiments of the
present invention to better understand the operation and components
thereof. Quotation marks are employed to highlight the first usage
of each term in the explanation discussed below.
[0046] A "breathing cycle" occurs when the patient first inhales
and then exhales; the breathing cycle commences when the patient
begins to inhale and terminates when the patient completes
exhalation. As a result, a breathing cycle consists of an
"inhalation interval" and an "exhalation interval" which follows
the inhalation interval. A convention used for explanation purposes
only of the exemplary embodiments of the present invention is that
the inhalation interval is sensed by detection of "negative
pressure values" relative to an ambient pressure environment which
is generated as the patient inhales and the exhalation interval is
sensed by detection of "positive pressure values" relative to the
ambient pressure environment which is generated as the patient
exhales. Particularly useful for explanation of the first exemplary
embodiment of the intermittent gas-insufflation apparatus of the
present invention is a "negative peak pressure value" which occurs
at the lowest pressure value detected during the inhalation
interval of the immediate breathing cycle and a "positive peak
pressure value" which occurs at the highest pressure value detected
during the exhalation interval of the immediate breathing cycle.
These negative and positive peak pressure values are employed for
the operation of the first exemplary embodiment of the intermittent
gas-insufflation apparatus of the present invention.
[0047] Furthermore, "immediate breathing cycle" and "successive
breathing cycle" are used herein as a convention only to explain
the operation of the present invention. As suggested by the terms
themselves, the immediate breathing cycle is the breathing cycle in
which the patient is currently breathing and the successive
breathing cycle follows the immediate breathing cycle. In reality,
once the "immediate breathing cycle" terminates, the "successive
breathing cycle" now becomes the immediate cycle and the
immediately terminated cycle then becomes the preceding breath
cycle. It would be understood by one of ordinary skilled in the art
that a patient breaths only during the immediate breathing cycle.
Additionally, "changes in breathing pressure" can be construed as
either actual changes of breathing pressure or changes in the rate
of breathing pressure.
[0048] A first exemplary embodiment of an intermittent
gas-insufflation apparatus 10 of the present invention with a
conserver 6 of the present invention is generally described with
reference to FIGS. 2 and 3. Intermittent gas-insufflation apparatus
10 is adapted to be disposed between and in fluid communication
with an oxygen supply or some other source 12 of treatment gas and
a breathing patient 14. In a present embodiment of the invention,
it is preferred that the treatment gas is oxygen although the
treatment gas could also be selected from a group consisting of
air, nitrous oxide, ether and other gases normally administered to
human beings and animals. Intermittent gas-insufflation apparatus
10 is operative to insufflate a quantity of the treatment gas into
an entrance 16 of a respiratory system of patient 14. Typically,
entrance 16 is a nose or mouth of patient 14, although, in some
instances, entrance 16 could be both the nose and the mouth of
patient 14. With reference to FIG. 3, the quantity of the treatment
gas (solid line) is continuously insufflated after an inhalation
interval 18 (dotted line below base line 20) and during an
exhalation interval 22 (dotted line above base line 20) of an
immediate breathing cycle 24. As stated above, immediate breathing
cycle 24 is inhalation interval 18 plus exhalation interval 22.
Insufflation of the treatment gas continues into a subsequent
inhalation interval 26 of a successive breathing cycle 28 of
patient 14.
[0049] It must be noted that the source 12 of treatment gas may be
implemented in a number of different ways without departing from
the invention as described herein. For example, and assuming for
purposes of illustration that the treatment gas is oxygen or air
with enriched levels of oxygen, the source 12 may be a liquid or
gaseous oxygen source, such as a tank of liquid oxygen or
pressurized gaseous oxygen or a tank of mixed gases in liquid or
gaseous form, or may be a concentrator, as is often employed when
the treatment gas is oxygen enriched air. As is well understood, a
conventional concentrator employs molecular sieves to selectively
absorb certain gases from the ambient air, such as nitrogen, so
that the resulting treatment gas has an increased proportional
oxygen level compared to the other remaining gases in the
mixture.
[0050] Again, with reference to FIG. 2, intermittent
gas-insufflation apparatus 10 includes a valve assembly 30, a
pressure transducer sensor 32, a microprocessor controller 34 and a
power source 35 which is operative to energize valve assembly 30,
sensor 32 and controller 34. Valve assembly 30 is disposed between
and in fluid communication with source 12 of treatment gas and
entrance 16 into the respiratory system of patient 14. Valve
assembly 30 is operative to actuate between a closed state and an
opened state. In the closed state, fluid communication is
interrupted so that the treatment gas is prevented from flowing
from source (e.g., oxygen supply) 12 of treatment gas to entrance
16 into the respiratory system of patient 14. In the opened state,
fluid communication is established so that the treatment gas flows
from source 12 of treatment gas to entrance 16 into the respiratory
system of patient 14.
[0051] For purposes of the present invention and the descriptions
thereof, valve assembly 30, sensor 32 and controller 34 may be
regarded as comprising a conserver 6 of the present invention. As
will be described in the following, the conserver 6 of the present
invention includes fundamental features and aspects of operation
that distinguish the conserver 6 over the conserver 6P of the prior
art and enable the conserver 6, according to the present invention,
to perform the desired functions of the present invention.
[0052] Sensor 32, in a form of a pressure transducer, is in fluid
communication with entrance 16 of the respiratory system of patient
14 and is operative to detect changes in breathing pressure
(represented by the dashed sinusoid line in FIG. 3) of breathing
patient 14 relative to an ambient pressure environment as patient
14 breaths. Although not by way of limitation, it is preferred, for
the first exemplary embodiment of the present invention, that the
detected changes in breathing pressure are actual changes in the
breathing pressure. Specifically, sensor 32 is operative to detect
changes in breathing pressure throughout inhalation and exhalation
intervals 18 and 22, respectively, of immediate breathing cycle 24
of patient 14. Sensor 32 is further operative to generate sensor
signals characteristic of the changes in breathing pressure of
immediate breathing cycle 24. These changes in breathing pressure,
plotted as a function of time (base line 20), is represented by the
dashed sinusoidal line shown in FIG. 3.
[0053] Controller 34 in a form of a microprocessor is coupled to
and between sensor 32 and valve assembly 30 (FIG. 2) and is
operative to receive and process the sensor signals to determine a
negative peak pressure value 36 (FIG. 3) which occurs during
inhalation interval 18 of the immediate breathing cycle 24 and a
positive peak pressure value 38 which occurs during exhalation
interval 22 of the immediate breathing cycle 24. Controller 34 is
responsive within exhalation interval 22 of immediate breathing
cycle 24 when a first predetermined percentage of positive peak
pressure value 38 is achieved which is discussed in more detail
below. Upon achieving the first predetermined percentage of
positive peak pressure value 38, valve assembly 30 is actuated to
the opened state so that the treatment gas flows from source 12 of
treatment gas to entrance 16 into the respiratory system of patient
14 during exhalation interval 22 of immediate breathing cycle 24
and during inhalation interval 18 of successive breathing cycle 28.
Controller 34 is further responsive within subsequent inhalation
interval 26 of successive breathing cycle 28, when a second
predetermined percentage of negative peak pressure value 36 is
achieved to actuate valve assembly 30 to the closed state so that
the treatment gas is prevented from flowing from source 12 of
treatment gas to entrance 16 into the respiratory system of patient
14.
[0054] Controller 34 is further responsive within subsequent
inhalation interval 26 of successive breathing cycle 28 when a
third predetermined percentage of negative peak pressure value BS
is achieved to further actuate valve assembly 30 into an enhanced
opened state. In the enhanced opened state, an additional quantity
of treatment gas flows from source 12 of treatment gas to entrance
16 into the respiratory system of patient 14 after exhalation
interval 22 of immediate breathing cycle 24 and before a remaining
portion of subsequent inhalation interval 26 of successive
breathing cycle 28. Alternatively, a single valve assembly 30 could
be actuated into the enhanced opened state during exhalation
interval 22 of immediate breathing cycle 24, if desired.
[0055] The first, second and third predetermined percentages are
determined clinically by a clinician for each individual patient.
Preferably, at least the first and second predetermined percentages
are tailored to respiratory needs of each individual patient
although the third predetermined percentage can be tailored to
respiratory needs of each individual patient. Thus, the
intermittent gas-insufflation apparatus of the present invention is
tailored to the patient's particular supplementary oxygen needs.
Factors which might be considered by the clinician are weight,
height, physical condition, severity of lung dysfunction and the
like. The first and second predetermined percentages are selected
from a range of 10% to 80%. The first and second predetermined
percentages are typically different from one another although they
could be the same. The first and second predetermined percentages
are selected from a range of 10% and 80% inclusive. Preferably, the
first predetermined percentage is 25%; the second predetermined
percentage is 33.3%. The third predetermined percentage is selected
from a range of 1% and 25% inclusive as long as it is less than the
second predetermined percentage. Preferably, the third
predetermined percentage is 12.5%.
[0056] For the first exemplary embodiment of intermittent
gas-insufflation apparatus 10 of the present invention, valve
assembly 30 includes a first solenoid valve V1 and a second
solenoid valve V2. First solenoid valve V1 is operative between a
first closed state and a first opened state; second solenoid valve
V2 is operative between a second closed state and a second opened
state. Each of first and second solenoid valves V1 and V2 is
independently connected in fluid communication to and between
source 12 of pressurized gas and entrance 16 to the respiratory
system of patient 14. Gas supply tubing 40 connects first and
second solenoid valves V1 and V2 to source 12 of pressurized
treatment gas. Respective ones of valve tubings 44 and 46 connect
first and second solenoid valves V1 and V2 to a manifold 48.
Manifold 48, in turn, is connected to a nasal cannula 50 via a
single gas delivery tube 52. First and second solenoid valves V1
and V2 are independently connected electrically to controller 34
via line 54 and 56 and to power source 35 via lines 58 and 60.
First and second solenoid valves V1 and V2 have a valve driver 62
interposed in respective lines 54 and 56 and each valve driver 62
is electrically connected to power source 35 via respective lines
64 and 66. Each valve driver 62 is electrically connected to
controller 34 via lines 67 and 69.
[0057] Nasal cannula 50, gas delivery tube 52 and a sensing tube 53
are components of a conventional cannula structure commonly known
in the art. In brief, nasal cannula 50 is sized and adopted to be
received by and secured proximate to the entrance of the
respiratory system of the breathing patient 14. Nasal cannula 50
has a septum, a partition or some other dividing or separating
structure (not shown) dividing or separates nasal cannula 50 into a
gas delivery conduit and a sensing conduit which are isolated from
fluid communication with one another. The gas delivery conduit is
in fluid communication with valve assembly 30 via gas delivery tube
52 and the sensing conduit is in fluid communication with sensor 32
via sensing tube 53. Thus, nasal cannula 50, sometimes referred to
as a divided or split cannula, can both detect changes in breathing
pressure and deliver oxygen to the patient simultaneously.
[0058] Again, with reference to FIGS. 2 and 3, first solenoid valve
V1 is operative to actuate from the first closed state to the first
opened state during exhalation interval 22 of immediate breathing
cycle 24 and from the first opened state to the first closed state
at a later stage "LS" of subsequent inhalation interval 26 of
successive breathing cycle 28. Thus, the treatment gas flows (solid
line) as shown during exhalation interval 22 of an immediate
breathing cycle 24 which begins at a waning stage "WS" of
exhalation interval of the immediate breathing cycle. Waning stage
"WS" represents the first predetermined percentage multiplied by a
positive peak pressure value 38. When in the first opened state,
the treatment gas flow builds to a steady state flow as shown by a
flat solid line portion 68 of flow trace 70. Meanwhile, second
solenoid valve V2 is actuated from the second closed state to the
second opened state at approximately a beginning stage "BS" of a
subsequent inhalation interval 26 of successive breathing cycle 28
thereby causing the enhanced opened state of valve assembly 30.
Beginning stage "BS" represents the third predetermined percentage
multiplied by the peak negative pressure value of the immediate
breathing cycle which is used in the subsequent inhalation
interval. In the second opened state of second solenoid valve V2,
the additional treatment gas flows as a high flow-rate pulse
reflected by the spiked solid line portion 72 of flow trace 70. The
second solenoid valve V2 is actuated from the second opened state
to the second closed state at later stage "LS" of subsequent
inhalation interval 26 of successive breathing cycle 28. Later
stage "LS" represents the second predetermined percentage
multiplied by the negative peak pressure value of the immediate
breathing cycle. Thus, although not by way of limitation, first
solenoid valve V1 and second solenoid valve V2 actuate to their
respective closed states simultaneously. Preferably, later stage
"LS" occurs before the negative peak pressure value of the
subsequent inhalation interval. Furthermore, first solenoid valve
V1 and second solenoid valve V2, respectively, actuate to the first
closed state and the second closed state when the second
predetermined percentage of negative peak pressure value 36 is
achieved. In any event, treatment gas flows at a flow rate selected
from a flow rate range of between 0.5 liters per minute and 12
liters per minute inclusive.
[0059] One of ordinary skill in the art would appreciate that the
intermittent gas-insufflation apparatus of the present invention
operates within its own operating cycle which is hereinafter deemed
an "insufflation operating cycle". The insufflation operating cycle
begins at the negative peak pressure value of the inhalation
interval of the immediate breathing cycle, continues through the
exhalation interval of the immediate breathing cycle and terminates
before the negative peak pressure value of a subsequent inhalation
interval of the successive breathing cycle. A skilled artisan would
understand that the insufflation operating cycle of the present
invention is considered to be phase shifted forward by 90 degrees
relative to the patient's normal breathing cycle. Additionally, one
of ordinary skill in the art would appreciate that the present
invention generates these negative and positive peak pressure
values to activate the present invention during the immediate
breathing cycle and utilizes reference pressures from the immediate
breathing cycle to de-activate the present invention during the
successive breathing cycle. Moreover, it is appreciated that the
intermittent gas insufflation apparatus of the present invention
detects changes in pressure, utilizes these detected pressure
changes for delivery of the treatment gas, and then commences
delivery of the treatment gas to the patient within the patient's
immediate breathing cycle, which has not heretofore been
accomplished by any of the prior art gas insufflation devices.
[0060] It follows from the first exemplary embodiment of
intermittent gas-insufflation apparatus 10 of the present
invention, a method can be employed for intermittently insufflating
a treatment gas from a pressurized treatment gas source 12 into
entrance 16 of a respiratory system of a breathing patient 14 after
inhalation interval 18 and during exhalation interval 22 of
immediate breathing cycle 24 and into subsequent inhalation
interval 26 of successive breathing cycle 28. The first step of
this method is determining the negative peak pressure value which
occurs during inhalation interval 18 of immediate breathing cycle
24. The next step is determining the positive peak pressure value
which occurs during exhalation interval 22 of immediate breathing
cycle 24. The next step includes commencing delivery of the
treatment gas to entrance 16 of the respiratory system of patient
14 during exhalation interval 22 of immediate breathing cycle 24
when the first predetermined percentage of positive peak pressure
value 38 is achieved. The next step includes continuing delivery of
the treatment gas to entrance 16 of the respiratory system during
subsequent inhalation interval 26 of successive breathing cycle 28.
The final step is ending delivery of the treatment gas to the
respiratory system during subsequent inhalation interval 26 of
successive breathing cycle 28 when a second predetermined
percentage of negative peak pressure value 36 is achieved.
Furthermore, the step of commencing delivery of additional
treatment gas to entrance 16 of the respiratory system of patient
14 during subsequent inhalation interval 26 of successive breathing
cycle 28 when a third predetermined percentage of negative peak
pressure value 36 is achieved can also be added after continuing
delivery of the treatment gas to entrance 16 of the respiratory
system during subsequent inhalation interval 26 of successive
breathing cycle 28.
[0061] A second exemplary embodiment of an intermittent
gas-insufflation apparatus employs a variable orifice valve, such
as a conventional tapered-needle valve. This second exemplary
embodiment of the intermittent gas-insufflation apparatus employs
the same general operational principles of the first exemplary
embodiment of the intermittent gas-insufflation apparatus 10 except
that a different type of valve is used in lieu of the first and
second solenoid valves. Also, the second exemplary embodiment of
the intermittent gas-insufflation apparatus requires some
modification to the software program which controls controller 34.
With modification to the software program, controller 34 is now
operative to receive and process the sensor signals generated by
sensor 32 during immediate breathing cycle 24 to calculate how much
of a quantity of the treatment gas is required by the breathing
effort of patient 14. For the second exemplary embodiment of the
present invention, it is preferred that sensor 32 detects a rate of
change of the breathing pressure of the patient. Controller 34 is
responsive to the sensor signals to actuate valve assembly 30 into
the opened state so that the calculated quantity of treatment gas
flows from source 12 of treatment gas to entrance 16 into the
respiratory system of patient 14 during exhalation interval 22 of
immediate breathing cycle 24 and into subsequent inhalation
interval 26 of successive breathing cycle 28. Controller 34 is
further responsive to actuate valve assembly 30 into the closed
state during subsequent inhalation interval 26 of successive
breathing cycle 28 when the calculated quantity of treatment gas is
delivered to entrance 16 into the respiratory system of patient 14.
It is preferred that valve assembly 30 actuates to the closed state
before the negative peak pressure value of the subsequent
inhalation interval of the successive breathing cycle is
achieved.
[0062] The calculated quantity of the treatment gas to be delivered
to the patient is predicated upon the immediate breathing cycle.
So, as the patient's respiratory needs change, for example, as a
result of increased physical activity, the calculated quantity of
the treatment gas will also increase. Correspondingly, when the
patient's physical activity decreases, changes in breathing
pressure will be detected and the calculated quantity of treatment
gas will also decrease.
[0063] The rate of change of pressure can be calculated by dividing
a difference between two detected pressure values by a difference
of respective times during which the pressure valves were detected.
This is illustrated in FIG. 3 by angles 71. A skilled artisan would
appreciate that this is a calculation of the "slope" of flow trace
70. Note that the rate of change of pressure can be calculated
during the inhalation interval of the immediate breathing cycle,
during the exhalation interval of the immediate breathing cycle or
even during the subsequent inhalation interval of the successive
breathing cycle.
[0064] Additionally, controller 34 is further operative to
determine a flow rate profile of the calculated quantity of the
treatment gas for continuous flow thereof to entrance 16 into the
respiratory system of the breathing patient during exhalation
interval 22 of immediate breathing cycle 24 and subsequent
inhalation interval 26 of successive breathing cycle 28. By way of
example only and not of limitation, the flow rate profile is
illustrated by the solid line flow trace 70 shown in FIG. 3. Since
modification of the software program can determine the
configuration of the flow rate profile as desired, the flow rate
profile is selected from a group consisting of a constant flow rate
profile as illustrated by flat solid line portion 68 of flow trace
70, a variable flow rate profile illustrated as the spiked solid
line portion of flow trace 70 or a combination the fixed and the
variable flow rate profile as illustrated in FIG. 3. Since the rate
of change of pressure can be detected within the subsequent
inhalation of the successive breathing cycle while the treatment
gas is flowing to the entrance of the respiratory system of the
patient, the flow rate profile of the flowing treatment gas can be
instantly changed to facilitate complete and timely delivery of the
calculated quantity of the treatment gas to the patient, if
desired. This feature of the present invention has not heretofore
been incorporated into any prior art. Obviously, the flow rate
profile could be instantly modified, if desired, at any time during
which the treatment gas is being delivered, i.e., during the
exhalation interval of the immediate breathing cycle and the
subsequently inhalation interval of the successive breathing
cycle.
[0065] By way of example only, a maximum flow rate "MFR" of the
calculated quantity of treatment gas flowing into entrance 16 of
the respiratory system of the breathing patient during exhalation
interval 22 of immediate breathing cycle 24 occurs shortly after
beginning stage "BS" of inhalation interval 18 of the subsequent
breathing cycle. Preferably, the flow rate profile of the treatment
gas includes a flow rate range having a minimum flow rate of 0.5
liters per minute and a maximum flow rate of 12.0 liters per
minute.
[0066] It follows from the second exemplary embodiment of the
intermittent gas insufflation apparatus of the present invention, a
method is employed for intermittently insufflating the treatment
gas from the pressurized treatment gas source and into an entrance
of a respiratory system of the breathing patient after the
inhalation interval and during the exhalation interval of the
immediate breathing cycle and into the subsequent inhalation
interval of the successive breathing cycle. The first step is
calculating the quantity of the treatment gas required to be
delivered to entrance 16 of the respiratory system of patient 14
during one of the inhalation interval 18 and the exhalation
interval 22 of immediate breathing cycle 24. The next step is
commencing delivery of the calculated quantity of the treatment gas
to entrance 16 of the respiratory system of patient 14 during
exhalation interval 22 of immediate breathing cycle 24. The next
step includes continuing delivery of the calculated quantity of the
treatment gas to entrance 16 of the respiratory system of patient
14 into subsequent inhalation interval 26 of successive breathing
cycle 28. The next step is ending delivery of the calculated
quantity of the treatment gas to the respiratory system of patient
14 when delivery is complete during subsequent inhalation interval
26 of successive breathing cycle 28. It is preferred that a step of
determining a desired flow rate profile for the delivery of the
quantity of the treatment gas occurs simultaneously with the step
of calculating the quantity of the treatment gas required to be
delivered to entrance 16 of the respiratory system of patient 14
during one of inhalation interval 18 and exhalation interval 22 of
immediate breathing cycle 24. It is also preferred that the step of
delivering a maximum flow rate of the desired flow rate profile
shortly after the beginning stage "BS" of subsequent inhalation
interval 26 of successive breathing cycle 28. Of course, it is
preferable to include a step of repeating the steps of this method
for each series of consecutive immediate and successive breathing
cycles.
[0067] A third exemplary embodiment of an intermittent
gas-insufflation apparatus of the present invention incorporates
valve assembly 30 which includes a shape-memory alloy-film actuated
valve (commonly referred to as a microflow valve). This third
exemplary embodiment of the intermittent gas insufflation apparatus
of the present invention employs the same operational principles of
the embodiments described above except that minor modifications of
the software program controlling controller 34 must be made. As
with any conventional shape-memory alloy-film actuated valve,
actuating this valve can be controlled whereby the opened state can
be varied, as dictated by the software program, as the treatment
gas flows from the source to the patient. Thus, flow rate of the
treatment gas can be precisely controlled at any time during
delivery of the treatment gas to the patient.
[0068] Given the three exemplary embodiments of the intermittent
gas insufflation apparatus of the present invention described
above, one of ordinary skill in the art would appreciate the
advancement made in the art. Particularly, the intermittent gas
insufflation apparatus of the present invention includes the
controller coupled to and between the sensor and the valve assembly
which is operative to receive and process the sensor signals
generated during either the inhalation interval of the immediate
breathing cycle, the exhalation interval of the immediate breathing
cycle or the inhalation and exhalation intervals of the immediate
breathing cycle. Although not by way of limitation, valve assembly
actuates to the opened state at waning stage "WS" of the exhalation
interval of the immediate breathing cycle and actuates to the
closed state during later stage "LS" of the subsequent inhalation
interval of the successive breathing cycle. Furthermore, the
intermittent gas insufflation apparatus of the present invention
employs a method for intermittently insufflating a treatment gas
from a pressurized treatment gas source and into an entrance of a
respiratory system of a breathing patient. The first step includes
generating sensor signals during either of the inhalation interval
of the immediate breathing cycle, the exhalation interval of the
immediate breathing cycle or both the inhalation and exhalation
intervals of the immediate breathing cycle. The next step includes
processing the sensor signals during either the inhalation interval
of the immediate breathing cycle, the exhalation interval of the
immediate breathing cycle or both of the inhalation and exhalation
intervals of the immediate breathing cycle to determine the
quantity of the treatment gas to be delivered to the entrance of
the respiratory system of the patient. The next step is then
commencing delivery of the quantity of treatment gas to the
entrance of the respiratory system of the patient during the
exhalation interval of the immediate breathing cycle. The following
step is continuing delivery of the quantity of the treatment gas to
the entrance of the respiratory system of the patient into the
subsequent inhalation interval of the successive breathing cycle.
The next step is ending delivery of the quantity of the treatment
gas to the respiratory system of the patient during the subsequent
inhalation interval of the successive breathing cycle.
[0069] A skilled artisan would comprehend that the valve assembly
can employ any type of valve, conventional or otherwise. Depending
upon the needs of the patient, the valve assembly could employ a
single solenoid valve, a single stepped solenoid valve, a single
proportional valve or a single shape-memory alloy-film actuated
valve. Also, for any of the exemplary embodiments described herein,
the present invention could incorporate an arrangement of solenoid
valves, an arrangement of stepped solenoid valves, an arrangement
of proportional valves, an arrangement of shape-memory alloy-film
actuated valves and even an arrangement of any combination of these
types of valves. Furthermore, the present invention could operate
with the valve or valves normally in the opened state or normally
in the closed state. Valves in the normally opened state would
provide a "fail-safe" feature for the valve assembly whereby, for
example, in the event of a power source failure, the valve or
valves of the valve assembly would automatically actuate to the
opened state. Thus, even without a power source, the patient would
continue to receive oxygen at a default rate of flow, preferably
about 2 liters per minute or some other desired flow rate.
[0070] Additionally, the intermittent gas insufflation apparatus of
the present invention could be used with a blood-oxygen
concentration device to maintain an appropriate blood-oxygen
concentration in a patient's blood stream. For example, with an
oximeter operably connected to a patient's ear, the software
program could again be modified so that the quantity of oxygen to
be delivered to the patient is based upon feedback from the
oximeter concerning the patient's blood-oxygen concentration or
content. Thus, a method is employed for maintaining at least a
threshold amount of blood-oxygen concentration in the patient
receiving supplemental oxygen from a supplemental oxygen delivery
system. The first step includes monitoring the amount of
blood-oxygen concentration in the patient. The next step is
determining if the amount of blood-oxygen concentration in the
patient is below the threshold amount of blood-oxygen
concentration. The next step is activating the supplemental oxygen
delivery system until the amount of blood-oxygen concentration is
at least the threshold amount of blood-oxygen concentration for the
patient.
[0071] Operation of the System
[0072] Again with reference to FIG. 2, the insufflation gas, in
this case oxygen, is supplied from source 12. The oxygen is
transmitted via gas supply tubing 40 to respective ones of first
and second solenoid valves V1 and V2. Via lines 44 and 46, the gas
communicates from first and second solenoid valves V1 and V2 with
manifold 48. From manifold 48, gas is transmitted via gas delivery
lube 52 to the nasal cannula 50. At least one sense tube 53 is also
connected to the cannula 50, preferably isolated from communication
with oxygen passing to the patient gas delivery tube 52. The
sensing tube 53 is connected to sensor 32 which is a pressure
transducer 32 supplied, for example, by SenSym Inc. of Palo Alto,
Calif. The pressure transducer 32 is powered by power source 35
which uses power line 78 to supply either 110VAC converted to 5VDC
by AC/DC, converter 80 or, alternatively, direct current from a
battery 82 which is connected electrically in line with a battery
low sensor 84 whose function will be more fully described
hereinafter. Additional power outputs from the power source 35 are
provided and designated PS. The PS power supply output is shown in
FIG. 2 to communicate, via electrical power via lines 58 and 60,
with first solenoid valve V1 and second solenoid valve V2. Power
source 35 also provides electrical power to the microprocessor 34
via line 79. The output line 86 of the pressure transducer is also
connected to an input in the microprocessor 34, which is also
labeled U1 in FIGS. 5A and 5B.
[0073] In operation, the sensing tube 53 will be under positive
pressure during a patient's exhalation and negative pressure during
a patient's inhalation when the nasal cannula 50 is fitted to a
normally breathing patient. Referring to FIG. 3, the top horizontal
sinusoidal line represents a trace of a patient's breathing cycle
where the curve above the straight horizontal line indicates the
positive pressure in the sensing tube 53 (base line 20 in FIG. 2)
during exhalation and the curve below the line represents the
negative pressure in the sensing tube 53 during inhalation. The
pressure differences over the period of a patient's breathing cycle
are sensed by the pressure transducer which directly communicates
with the pressure of the gas in the sensing tube 53. Typically, the
pressure transducer will provide a proportional analog signal
having positive and negative voltage values representative of the
positive and negative pressure variants of a patient's exhalation
and inhalation as shown by the graph on FIG. 3. This signal is fed
via output line 86 to the microprocessor 34 or U1.
[0074] In the microprocessor 34 or U1, the positive and negative
voltage containing signal stream or waveform is converted into a
digital format and is continuously stored in the random access
memory of the microprocessor U1. The stored digital signal is
accessed continuously during the operation of the device for
determination of the occurrence of various preselected conditions
which actuate or trigger the operation of first and second solenoid
valves V1 and V2. During the exhalation interval (see FIG. 3) of
the immediate breathing cycle, the maximum positive pressure is
indicated at positive peak pressure value 38. When the software in
the microprocessor 34 or U1 verifies that a maximum value is
reached, a predetermined fraction of that signal value is created
by the microprocessor and the digitized, stored waveform signal is
interrogated and compared with that created value. When that value
is reached, an enable signal is produced in the microprocessor to
activate valve driver 62 which, in turn, actuates first solenoid
valve V1 opening it to the source 12 of oxygen via tubing 40 and
the nasal cannula 50 via valve tubing 44 and 46 of respective ones
of first and second solenoid valves V1 and V2 and gas delivery tube
52. The rate of flow of the oxygen is regulated by the size of an
orifice (not shown) inherent in the valve and is typically about 2
liters per minute for first solenoid valve V1 although other sizes
are possible.
[0075] Another preselected fraction of the maximum negative
inhalation pressure is sensed. This value can be set by the
respiratory therapist or patient to accommodate changes in physical
activity and the set points will have been predetermined for each
patient by monitoring blood gases during selected activities.
Within the limits of adjustability of an amount of oxygen to be
delivered, there can be incorporated in such a fixed flow device a
degree of patient need accommodation not hitherto obtained.
[0076] Likewise, second solenoid valve V2 can be replaced with a
variable orifice (not shown) or variable flow valve (not shown)
which can be programmed to deliver the predetermined amount of
oxygen insufflation gas during the inhalation interval before the
predicted maximum negative pressure so as to take full advantage of
the benefits and advantages of the present invention.
[0077] This oxygen continues to flow to the patient until the point
in the breathing cycle when trigger point "LS" is reached. The
trigger point is generated by the microprocessor 34 or U1 when the
value of the pressure transducer output reaches a preselected
fractional value of the peak value of the inhalation interval of
the immediate breathing cycle, which was determined and stored by
the microprocessor at the peak of the inhalation interval during
the immediate breathing cycle. Contemporaneously, the second enable
signal is routed to valve driver 62 which is energized/actuated
causing oxygen to flow from gas supply tubing 40 and through valve
tubing 46 from whence it exits through the gas delivery tube 52 to
the patient. The rate of flow of oxygen is determined by the size
of an orifice restrictor at the valve seat (not shown) of second
solenoid valve V2. This oxygen flow continues until 33%, for
example, of the peak negative pressure value of the inhalation
interval of the immediate breathing cycle is reached in the
subsequent inhalation interval. Simultaneously, the microprocessor
34 or U1 will be measuring the present inhalation interval to
calculate and store the trigger point value, i.e., 33% of the
negative peak pressure value of the immediate inhalation interval,
for the generation of the next trigger point which is required
during the succeeding breathing cycle.
[0078] The sequence described hereinbefore for the embodiments is
repeated for each breathing cycle. If the patient's need for oxygen
increases, e.g., from exertion or exercise, the appropriately
programmed present invention automatically accommodates the
increased need by delivering a predetermined amount of oxygen for
each exhalation/inhalation interval of each breathing cycle.
Operation of the present invention is further facilitated by the
following switches, lights and an alarm. These are shown in FIGS.
5A and 5B:
[0079] (a) "TEST" Switch, TS-1, is a multi position digital switch
which can be used by the operator to run a series of functional
tests on the device to check its operation prior to placing the
device into use with a patient. These tests can also be used as a
diagnostic tool in the event of equipment malfunction.
[0080] (b) "LO BPM" is the label placed on light L-1, designating
"Low Breaths Per Minute". This light is illuminated by a signal
from the microprocessor 34 or U1 when the patient's breathing rate
decreases to an unsafe level.
[0081] (c) "ALARM" A-1 is sounded by a signal from the
microprocessor 34 or U1 whenever the breathing rate is too low as
determined in (b) above, or when the battery voltage decreases
below a preset level which would provide for correct operation of
the device. The present invention might include a switch so that
when the alarm sounds, the patient could manually switch to the
default rate of flow.
[0082] (d) "VALVE ON" light L-2 is a green light connected across
either one or both of the solenoid valves, so that the light is
illuminated whenever the valves or valve is activated thereby
signaling the cycling of the valve(s) with each breath.
[0083] (e) "LO BAT" L-3 is the low battery light. This red light is
illuminated by a signal from the microprocessor 34 or U1 at the
same time that the ALARM is sounded. Additionally, this provides
the information that the alarm is sounded, e.g., because the
battery voltage was low and not that the patient was having
breathing difficulty. Again, the patient may employ the switch for
the default rate of flow when the low Battery light
illuminates.
DETAILED DESCRIPTION OF CIRCUITS
Power Source
[0084] With reference to FIG. 4, the present invention is normally
powered using 110VAC which is converted to 9VDC via the AC/DC
converter 80. The 9VDC trickle charges the battery 82 through the
charging resistor R17. The value of R17 is selected to prevent
damage to the battery. When the AC/DC converter is unplugged from
the system, the battery B1 provides backup power to the system. The
diode D2 bypasses the charging resistor R17 to enable adequate
system power in the backup mode. Capacitor C10 stores sufficient
charge to supplement any large power demands when the solenoid
valves are activated. The 9VDC is applied to the step-clown DC--DC
converter circuit DC which provides .sup.+5VDC regulated power to
the electronic circuits when switch SW1 is in the 0N position. The
9VDC is also applied to the solenoid valves V1 and V2. Converter DC
is configured as a step-down converter. The resistor R19 is
selected to limit the maximum output current at .sup.+5VDC. The
filter circuit comprised of diode D3, inductor L4, and capacitor
C11, smooths the output ripple to an acceptable level. Regulation
is provided by feeding back the output signal to the SENSE input,
pin 8, of the DC--DC converter. A low battery signal is generated
in the DC--DC converter. The trip point is determined by the value
of resistor R18, and the network of resistors R20, R21 and R22. The
low battery signal AO is provided at pin 6 of the DC--DC converter
and sent to the microprocessor input pin 34-P3.3, as shown in FIG.
5A.
[0085] Valve Driver/Power Saver
[0086] In FIG. 5B, the microprocessor 34 or U1 provides turn-on
signals to actuate solenoid valves V1 and V2. The valves will
remain actuated as long as the turn-on signal is present. The drive
circuitry for the solenoid valve V1 consists of a MOS-FET
semiconductor Q1 to actuate solenoid valve V1, and a MOS-FET Q3
with a resistor R15, to hold the valve in the actuated position at
reduced power. The power saving feature operates by switching the
turn-on signal from Q1 to Q3 immediately after the solenoid valve
is actuated. The current required to hold the solenoid valve
actuated is less than the current required for actuation and is set
by selecting the value of R15. The diode D1 clamps the voltage
across the solenoid valve to prevent arcing and overshoot.
Similarly, the drive circuitry for the solenoid valve V2 consists
of MOS-FETs Q2, Q4 and resistor R16. A light emitting diode L2, and
its current limiting resistor R6, are placed across solenoid valve
V2, to indicate that the valve has been actuated. Each turn-on
signal will result in the illumination of the light emitting diode
for the duration of the signal.
[0087] Alarm
[0088] In FIGS. 2 and 5B, the alarm is a piezoelectric device that
emits an audible sound when activated by the microprocessor. The
combinations of conditions to cause an alarm are programmed into
the microprocessor. The alarm is sounded when any of the
predetermined conditions are sensed.
[0089] Diagnostic Outputs
[0090] Signals are available to aid in data logging and
troubleshooting. These signals can be accessed and displayed with
the use of auxiliary equipment such as an oscilloscope, a chart
recorder, etc.
[0091] Digital Switch
[0092] In FIGS. 2 and 5A, the digital switch TS-1 is a
multi-position rotary switch that provides a four digit binary
coded decimal (BCD) output. The output of the BCD switch is
connected to the microprocessor at pins 35, 36, 37 and 38. The
selected codes will address preprogrammed diagnostic routines that
will perform calibration, system setup and diagnostic
operations.
[0093] Reference Voltage Generator
[0094] In FIG. 5A, the reference voltage generator circuit consists
of a reference voltage and operational amplifier C. Resistor R1
provides the feedback for the amplifier C. Resistors R2, R3 and POT
R4 provide input resistance. POT R4 provides adjustability of the
reference voltage output.
[0095] The precision reference voltage is utilized by the micro
controller analog to digital converter for its reference voltage.
Also, the reference voltage provides a precision and stable voltage
to the pressure transducer bridge circuit.
[0096] The offset bias voltage utilized by the pressure transducer
circuit is provided at the center tap of POT R5. The voltage is
adjustable between 0 volts and the reference voltage.
[0097] Pressure Transducer Circuit
[0098] Also in FIG. 5A, the pressure transducer circuit consists of
a standard differential pressure transducer 32 and differential
amplifiers A and B. The pressure transducer is a typical variable
resistance bridge circuit. The outputs of transducer 32 are
connected to operational amplifiers A and B via output pins 5 and
3, respectively. Pin 2 is the reference voltage line and pin 4 is
the return input (ground).
[0099] The operational amplifiers A and B are each configured as a
differential amplifier with high gain. The offset bias voltage
provides an offset output voltage at pin 7 of B also defined as
ASIg. The output ASIg is adjusted for 1/2 the reference voltage at
ambient pressure. The offset voltage provides a means to output
positive and negative pressure measurements.
[0100] Micro Controller
[0101] The microprocessor U1 or 34, also known as micro controller,
is a standard Intel Part MC80C51 GB, for example. The basic
features are the following:
[0102] 8 bit computer architecture;
[0103] 256 random access memory;
[0104] 4K programmable memory; and
[0105] 8 channels of analog to digital conversion.
[0106] The crystal (XTAL), attached at pins 52 and 53, provides the
control of the operating frequency for the micro controller. The
reference voltage generator provides a power on reset signal
(RESET) to the microprocessor. The signal is set to a low voltage
upon initial power turn-on. The microprocessor is held inactive
until the signal goes to a logic high level. At this time, the
microprocessor starts executing stored programmed instructions. The
process flow is discussed hereinafter. The input signals to the
microprocessor are the analog pressure transducer signal Asig and
digital signal Battery Lo (pin 34-P3.3). The Asig are inputted to
the first four analog channels for digital conversion ACH0-pin 49,
ACH1-pin 48, ACH2-pin 47, ACH3-pin 46.
[0107] Outputs from the microprocessor are the following digital
signals (see FIG. 5B). P1.0-pin 22 and P1.1-pin 23. P1.0 commands
the valve driver circuit V2 and P1.1 commands the valve driver
circuit V1.
[0108] Output at P1.7-pin 29 is connected to an audible alarm
(e.g., a buzzer) A-1. The microprocessor generates various audible
frequencies to denote different alarm indications. The output
P1.6-pin 28, P1.5-pin 27 drive light emitting diodes (LED) to
indicate low breathing rate and Battery Lo voltage,
respectively.
[0109] Program Flow
[0110] The following describes the process flow that will be coded
into the micro controller. FIGS. 6A and 6B show the flow of the
process that monitors the exhalation and inhalation pressures in
real-time and processes this information to determine the start and
stop time for turning on and off the O.sub.2 valves.
[0111] Upon completion of the power-on reset, the stored program
initializes the microprocessor. The initialization 101 consists of
setting up the 10 ms interrupts timer, baud rate timer, serial
port, A/D converter and input/output ports of the microprocessor.
Once initialization has been completed, the program enters the main
program 102. The main program starts with a check of the Battery Lo
signal P3.3 at step 103. If the battery voltage level low is
detected, the processor goes to the alarm routine at step 104. The
processor turns on the Lo Battery LED indicator and also starts a
low frequency beep on the audible alarm. Once completed, the
program continues and goes into a wait mode at Step 105.
[0112] Upon receipt of a 10 ms interrupt, the program services the
interrupt routine at step 106. This involves starting the
analog-to-digital conversion and reset in the interrupt timer. The
next step is to read the four analog converted voltages at 107
after a fixed time delay from the start of A/D conversion. This is
to make sure conversion is complete. The four valves are averaged
and labeled present value. The present value is stored at 108 into
the last byte of the last in-first out (LIFO) memory of 16 bytes.
Slopes are calculated 109 either as values or as indicators
(positive or negative). Slopes are calculated between first and
last, last and third to last, last and fifth to last, and third to
last, and fifth to last. The flow continues by monitoring present
value with the last highest value at step 110. If the present value
is greater than the last highest value, the peak value is updated
with the present value. If the present value is less than the peak
value, the peak value is unchanged. To determine if a peak has been
detected, the following conditions must be present:
[0113] 1) the long slope must be negative (slope first to
last);
[0114] 2) the short slope must be negative (slope fifth to last and
last);
[0115] 3) in exhalation interval of the cycle.
[0116] If peak detection is enabled, the next step is to retrieve
the peak value at step 111 and divide by 4 to get 25% of the peak
value. This then becomes the start value for purge on.
[0117] The detection of the minimum value at 112 is very similar to
the peak detection process with the following differences. Minimum
detection criteria is the following:
[0118] 1) the long-slope must be positive;
[0119] 2) the short-slope must be positive;
[0120] 3) in inhalation interval of the cycle.
[0121] When minimum detection has been detected, the minimum value
is retrieved at 113, 114 and 12.5% and 331/3% values are calculated
and stored. These values are used for start of the main O.sub.2
burst and turn-off on the next inhalation cycle. During the O.sub.2
cycle in which the peak detection occurs, the 25% value of the peak
is stored at step 115 and compared with the present pressure value.
If the present value is less than or equal to the 25% value of
peak, the microprocessor commands the valve driver V1 on at step
116. The V1 valve opens and provides a 2 L/M flow rate to purge the
O.sub.2 line.
[0122] During the same cycle and during the inhalation period, the
processor compares the present pressure value with the 12.5%
minimum value of the previous cycle at step 117. When the present
pressure value equals or is less than the 12.5 minimum value, the
microprocessor turns on the high flow valve V2 at step 118.
[0123] The valves are turned off when the present pressure value is
greater or equal to 331/3% of the minimum value of the previous
cycle at steps 119, 120. The end of the main program flow, at step
121, shifts the LIFO memory by one byte for set up of the next 10
ms measurement.
[0124] Also, the watch dog timer is reset. The watch dog timer
reinitializes the microprocessor if, for some reason, the program
does not reset the watch dog timer.
[0125] The flow continues by monitoring the inhalation cycles. When
no inhalation is detected, the microprocessor will turn on the
audible alarm and LED indicator. Also, the Lo flow valve V1 will be
enabled to provide continuous Lo O.sub.2 flow.
[0126] The program flow continues with the process by returning to
the start of main program and waiting for the 10 ms interrupt.
[0127] The intermittent gas-insufflation apparatus of the present
invention provides significant advancements and benefits over the
prior art. The intermittent gas-insufflation apparatus of the
present invention determines the appropriate quantity of oxygen to
be delivered to the patient during an immediate breathing cycle and
adjusts appropriately to supply the quantity of oxygen commensurate
with the physical activity of the patient.
[0128] The intermittent gas-insufflation apparatus delivers the
appropriate quantity of oxygen continuously during an exhalation
interval of the immediate breathing cycle and into an inhalation
interval of a subsequent breathing cycle. This results in purging
some of the air remaining in the nasal passage from the prior
breath and enriches a remaining portion thereof. Further, a
high-rate pulse of oxygen is delivered at approximately the
beginning of the subsequent inhalation interval of the successive
breathing cycle which is optimum. The intermittent gas-insufflation
apparatus can determine an appropriate flow rate profile for
delivering the oxygen during the exhalation interval of the
immediate breathing cycle and the inhalation interval of the
successive breathing cycle and, if desired, can modify the flow
rate profile even while oxygen is being delivered to the patient.
The intermittent gas-insufflation apparatus can terminate delivery
of oxygen during the subsequent inhalation interval of the
successive breathing cycle and, preferably before the negative peak
pressure value generated in the immediate breathing cycle is
reached in the successive breathing cycle. This feature conserves
utilization of costly oxygen, particularly since oxygen is
delivered when it could be best utilized by the patient.
[0129] As can be seen in FIGS. 2 and 5A, the system and method of
the present invention relate to one or more transducers which
detect or sense, due to pressure variations, the end of an
exhalation breath and the beginning of an inhalation breath of a
patient. The system is designed to predict the beginning of the
next subsequent inhalation and activate delivery of the bolus
during approximately the last 10% of the exhalation breath which is
immediately prior to the next inhalation breath of the patient.
Such deliver provides the system and method with a sufficiently
amount of oxygen or room air, with an increased concentration of
oxygen, along the oxygen supply tubing or conduit and to a patient
interface, such a cannula with a pair of nares for positioning
within the nostrils of the patient and delivery of the treatment
gas or a divided cannula having a pair of nares in which a first
one of the pair of nares communicates with the treatment gas to one
of the nostrils and a second one of the pair of nares communicates
with a sensing device for sensing pressure in the other nostril of
the patient. The treatment gas is exhausted out through opening in
the nares and enters into those nasal and/or mouth cavities and
dilutes the concentration of carbon dioxide as well as enrich the
concentration of oxygen of the exhaled gases contained in those
cavities or areas so that when the patient commences the next
inhalation breath, the gases initially inhaled by the patient
contains a sufficiently diluted concentration of carbon dioxide as
well as a sufficiently enriched concentration of oxygen.
[0130] Upon activation of the oxygen concentration system and
method for a detected or sensed breathing cycle, the supply of
oxygen, e.g., room air with a concentrated or increased level of
oxygen, to the patient may continue for the entire remainder of the
inhalation breath. In a preferred form of the system and method,
the supply of oxygen may be discontinued prior to completion of the
inhalation breath of the patient, e.g., during approximately the
last 10% or so of the patient's inhalation breath, since the later
portion of the supplied oxygen generally only actual reaches the
nasal and/or mouth cavities or possibly the trachea at the time the
patient's inhalation ceases and thus does not reach the lungs of
the patient and is wasted. The discontinuance of the oxygen supply,
prior to completion of inhalation, still results in both an
adequate oxygen supply as well as conservation of oxygen.
[0131] Failsafe Modes of Operation
[0132] As discussed herein above, the conserver 6 of the present
invention includes a method and apparatus for maintaining an
acceptable level of treatment gas in the patient under fault
conditions, such as a loss of inhalation/exhalation data from the
patient or a loss of power in the system.
[0133] These methods and apparatus are illustrated, for example, in
FIGS. 7 and 8, and are referred to as "failsafe" mechanisms or
methods and operate to ensure an adequate level of treatment gas
saturation in the patent. In a first failsafe mode, which may be
referred to as a patient data failure mode, the system is required
to maintain the desired level of treatment gas in the patient when
the breathing cycle of the patient, that is, either an inhalation
or exhalation breathing interval, can not be sensed or detected by
the sensing device 32.
[0134] A second failsafe mode may be referred to as a system
failure mode and may arise, for example, when there is a power
failure in the apparatus, whether for internal or external reasons,
or when at least some element of the system develops an operational
fault or fails outright.
[0135] Again, the object of both the first and second failure modes
of operation is to maintain an acceptable level of treatment gas in
the patient under the fault conditions while also using as little
power and oxygen as is necessary to maintain the desired level of
treatment gas in the patient under the patient's current
requirements, which will depend upon such factors as the patient's
current condition, such as asleep or awake, and activity level.
[0136] Patient Data Failure Mode 124
[0137] First considering the patient data failure mode of operation
as illustrated in FIG. 7, the conserver 6 enters patient data
failure mode 124 when, in step 126, at least one sensing device 32,
such as a transducer, a pneumatic diaphragm or some other sensing
or detecting device 32, is unable to detect or sense the beginning
or ending of an inhalation or exhalation breath of a patient 14. In
patient data failure mode 124, the conserver 6 and method will
assume that the patient 14 is still alive and breathing and will
automatically switch to the data failure mode of failsafe operation
to maintain an adequate level of treatment gas saturation in the
patient under the patient's current condition and level of activity
while conserving both the supply of treatment gas and power levels
in the system.
[0138] In a first step 128 of the patient data failure mode 124 of
operation, the conserver 6 will continue cycle the supply of oxygen
to the patient in a periodic "on" and "off" cycle at a preselected
number of cycles per minute wherein the selected cycle rate may be
determined by the patient's previously established requirements,
which may be adjusted from time to time, depending upon the
patient's anticipated activity, such as sleeping, or may depend on
such factors the patent's last known oxygen requirements. The
patient's last known oxygen cycle rate and oxygen flow rate and
oxygen concentration requirements will in turn typically depend,
for example, upon the patient's last known breathing cycle rate and
condition and level of activity, such as whether the patient 14 was
sleeping or awake but at rest or was physically active.
[0139] First assuming that the patient's required cycle rate is
preselected, as described briefly above, and as described above,
the conserver 6 will enter the patient data failure mode 124 at
step 126, at which point the patient 14 breathing cycle information
will not be available to the conserver 6. The on/off cycle rate of
the conserver 6 must therefore be selected to provide the desired
level of treatment gas to the patient even when the period of the
on/off cycle does not precisely match that of the patient's
breathing cycle and even when the on/off cycle is not synchronized
with the patient's inhalation and exhalation intervals. Stated
another way, the period and duration of the on cycle of the
conserver 6 must be selected such that the uncoordinated and
unsynchronized overlap between the on interval of the conserver 6
cycle, that is, the periodic interval during which the treatment
gas is effectively delivered to the patient 14, and the patient 14
actual breathing cycle interval during which the patient 14
effectively receives the treatment gas, must be sufficient to
maintain the desired level of treatment gas in the patient 14.
Again, the period and duration of the conserver 6 on interval will
be dependent upon the state or activity of the patient, e.g., is
the patient at rest, sleeping, walking, exercising, etc.
[0140] According to a present embodiment of the present invention,
it has been determined that cycling the supply of oxygen or other
treatment gas to the patient 14 "on" and "off" at a rate of between
about 10 to 40 times per minute and typically about 20 times per
minute will adequately saturate the patient with oxygen, e.g.,
maintain the patient at an oxygen saturation level of about 92% to
93%, while the patient is at rest or sleeping. This on/off cycle
rate generally is not sufficient, however, when the patient is
undergoing any significant activity. If the patient is undergoing
activity, an increased number of "on" and "off" cycles per minute,
e.g., 30-50 cycles per minute, may be required in order to obtain a
blood oxygen saturation level of the patient at approximately 92%
to 93%.
[0141] Assuming that the failsafe gas delivery cycle is
predetermined and fixed, in step 128 the conserver 6 will enter a
fixed delivery process 130 wherein the treatment gas, such as
oxygen, is delivered to the patient 14 in a failure delivery cycle
132 (FIG. 8) having fixed intervals of gas delivery 134 and gas
non-delivery 136. Assuming that the system is to operate during the
patient data failure mode at a cycle rate of 20 cycles per minute,
the system and method will then begin delivering oxygen to the
patient in successive failure delivery cycles 132, each failure
delivery cycle 132 having a period of approximately 3 seconds,
which corresponds to a cyclic rate of 20 cycles per minute. As
illustrated in FIG. 8, the oxygen will be delivered to the patient
14 during each 3 second failure delivery cycle 132, the treatment
gas being provided to the patient 14 during a gas delivery interval
134 of about 1 second or so and then turned off for a subsequent
gas non-delivery interval 136 of about 2 seconds or so. It has been
found that in this mode of operation, the overlap between the
periods when gas is delivered to the patient 14 and the periods
when the patient 14 is, in fact, accepting the gas for a beneficial
result sufficiently overlap to maintain the patient 14 at the
desired levels of treatment gas saturation.
[0142] As indicated in FIG. 7, the conserver 6 will periodically
attempt, in step 139, to determine whether the conserver 6 is still
unable to detect or sense breathing of the patient, which may
occur, for example, at the end of each 3 second failure delivery
cycle 132 or during the non-delivery interval 136 of each failure
delivery cycle 132 and, if no breathing cycle or inhalation or
exhalation interval is detected, the conserver 6 will return to
step 126 to continue in patient data failure mode 124. The failsafe
mechanism will continuously repeat this routine until the system
and method is either turned off or is finally able to detect or
sense breathing of the patient.
[0143] In the event that the conserver 6 is turned "off" when the
conserver is operating in the patient data failure mode 124, the
conserver 6 will cease operating and the supply of oxygen will be
completely discontinued. In the event that the conserver 6 is left
in the "on" state and continues to operate in patient data failure
mode 124 and patient breathing is again detected in step 139, the
conserver 6 will return, at step 142, to normal operation 140 and
the conserver 6 and will again automatically supply oxygen at the
end of the exhalation intervals and prior to commencement of the
inhalation intervals as described herein above.
[0144] As described herein above, the operation of conserver 6 and
the patient data failure mode 124 method of operation of the
present invention may be extended through additional steps and
processes. For example, controller 34 of conserver 6 may include a
rate memory 144 that determines and averages information regarding
the patient 14 breathing cycle over a time progressive sampling
window 146 that determines, for example, the average breathing
cycle period and the average lengths of the inhalation and
exhalation intervals within the sampling window 146 period. This
information may then be used to determine the current requirements
of the patient 14 when the conserver 6 enters the patient data
failure mode 124 as, for example, percentages of the average
breathing cycle period and the average lengths of the inhalation
and exhalation intervals determines within the sampling window 146
period, which is terminated at the time conserver 6 detects the
failure in patient data and enter patient data failure mode 124.
According to this method of operation in patient data failure mode
124, therefore, the period of failure delivery cycle 132 and the
lengths of gas delivery interval 134 and gas non-delivery interval
136 are not fixed, but are instead continuously adjusted or adapted
according to the actual breathing requirements of the patient.
[0145] In yet another extension to the operation of conserver 6 and
to the patient data failure mode 124 operation of the present
invention, that is, in addition to either or both of the features
of the above described patient data failure modes of operation, the
conserver 6 may further include facilities for detecting a current
activity level of the patient 14. For example, a conserver 6 of the
present invention may include a connection detector or sensor 148
(FIG. 2) for determining whether the conserver 6 is connected into
the system 10 or has been mechanically disconnected from the system
10, as when the patient 14 is moving about by means of extensions
of gas delivery tube 52 and sensing tube 53 and is thereby possibly
in an active state, or at least is not passively resting or asleep.
Similar purposes may be met by the addition of a motion sensor 150
(FIG. 2) to conserver 6, which may then indicate whether the
patient 14 is possibly in an active state or not, or is probably in
a passive resting state or asleep, by detecting motion of the
conserver 6, which would normally be in motion only when the
patient 14 is physically active.
[0146] The response of the conserver 6 to the activity level of the
patient 14 when the conserver 6 enters the patient data failure
mode 124 is thereby more directly dependent upon the apparent
activity level of the patient 14, as are the treatment gas
requirements of the patient 14 for various patient activity levels.
It will also be noted that the degree of reliability in
interpreting the motion indications from, for example, the
connection detector or sensor 148 or the motion sensor 150, will
depend upon the means by which conserver 6 motion and this,
hopefully, patient 14 activity, is detected. For example, the
connection detector 148 is probably less reliability indicative of
a patient's activity than the motion sensor 150 because a conserver
6 may operate remotely from the apparatus 10 for a number of
reasons that do not reflect a higher level of activity, such as
comfort while watching television or reading a book. In contrast,
the motion sensor 150 of the conserver 6 detects and indicates
actual movement of the conserver 6, which is usually the system
element most closely associated with the patient 14 and which
thereby more reliably indicates whether the conserver 6, and thus
the patient 14, is actually in an active state. Also, no motion of
the conserver 6 will be indicated unless there is actual motion of
the conserver 6, thereby eliminating one more areas of
uncertainty.
[0147] The action taken by conserver 6 as a result of the patient
14 activity level will, of course, depend upon the condition and
problems of the patient 14 and, for example, on the needs of the
patient 14 as a result of the range of activity normally engaged in
by the patient 14. For example, the requirement of a patient 14
whose activities range from sleeping to sitting in a wheelchair
will be much narrower, and the peak will be much lower, than those
of a patient 14 having a more active life. In certain instances,
therefore, the conserver 6 may respond to a measurement of probably
patient activity level for a given patient 14 by delivering
treatment gas to the patient only during every other delivery cycle
132, or possible every second or third delivery cycle, as this
delivery rate may be sufficient to maintain the necessary levels of
treatment gas in the patient's system. In other instances, however,
the conserver 6 may respond to an activity measurement for a given
patient 14 by delivering treatment gas to the patient 14 during
each delivery cycle 132 in order to maintain the desired treatment
gas levels in the patient 14.
[0148] In either instance, however, the conserver 6 may include
consideration of the patient's apparent activity level in
determining the level of treatment gas delivered to the patient
14.
[0149] System Failure Mode 152
[0150] As described above, conserver 6 may further support a second
failsafe mode referred to as system failure mode 152, which may
arise, for example, when there is a power failure in the apparatus,
whether for internal or external reasons, or when at least some
elements of the system develop operational faults or fail
outright.
[0151] As illustrated in FIG. 7, conserver 6 will exit normal
operation 140 and will enter system failure mode 152 at a step 154
when conserver 6 detects that the battery or other power supply
device for the conserver 6 has failed or malfunctions or is
inadequately low on power, or if such condition is pending, or if
conserver 6 detects that another component of the conserver 6 has
failed or malfunctions for some reason, or has a pending failure or
malfunction. For example, the conserver 6 may detect that a line
current power supply is not connected to a power line and that the
reserve power stored in a battery power supply is decreasing at an
abnormal rate or for an abnormal period or has fallen below a lower
limit.
[0152] In step 154, a conserver 6 of the present invention will
switch to system failure mode 152 in which conserver 6 operates in
a continuous delivery mode to provide a continuous flow of
treatment gas to the patient 14. In continuous delivery mode a
valve is switched to an open state whereby the treatment gas, such
as oxygen or room air or a mixture of gases, are continuously
delivered to the patient 14 at a preset delivery rate, e.g.,
typically ranging between 1.5 and 6 liters per minute. As a result
of this continuous supply of treatment gas, the conserver 6 no
longer conserves the treatment gas delivered to the patient 14,
such as oxygen or room air with an increased concentration of
oxygen, but the patient is nevertheless still supplied with a
sufficient amount of treatment gals so that the patient is, for
example, adequately saturated with oxygen to achieve an oxygen
blood saturation level of approximately 92% to 93%.
[0153] In this regard, it has been described herein above and
illustrated in FIG. 2, for example, that a conserver 6 of the
present invention includes a valve assembly 30 having a first
solenoid valve V1 and a second solenoid valve V2 wherein first
solenoid valve V1 is operative between a first closed state and a
first opened state and second solenoid valve V2 is operative
between a second closed state and a second opened state. Each of
solenoid valves V1 and V2 is independently connected by gas supply
tubing 40 in fluid communication to and between source 12 of the
treatment gas and an entrance 16 into the respiratory system of
patient 14. Respective ones of valve tubings 44 and 46 connect
solenoid valves; V1 and V2 to manifold 48 which, in turn, is
connected to a nasal cannula 50 via a single gas delivery tube 52.
Solenoid valves V1 and V2 are independently connected electrically
to controller 34 via line 54 and 56 and to power source 35 via
lines 58 and 60 and have a valve driver 62 interposed in respective
lines 54 and 56 wherein each valve driver 62 is electrically
connected to power source 35 via respective lines 64 and 66. Each
valve driver 62 is, in turn, electrically connected to controller
34 via lines 67 and 69.
[0154] As has also been described with reference to FIG. 2,
solenoid valve V1 is operative to actuate from the first closed
state to the first opened state during exhalation interval 22 of
immediate breathing cycle 24 and from the first opened state to the
first closed state at a later stage "LS" of subsequent inhalation
interval 26 of successive breathing cycle 28. Thus, the treatment
gas flows (solid line) as shown during exhalation interval 22 of
immediate breathing cycle 24 which begins at a waning stage "WS" of
exhalation interval of the immediate breathing cycle. Waning stage
"WS" represents the first predetermined percentage multiplied by
positive peak pressure value 38. When in the first opened state,
the treatment gas flow builds to a steady state flow as shown by a
flat solid line portion 68 of flow trace 70. Meanwhile, second
solenoid valve V2 is operative to actuate from the second closed
state to the second opened state at approximately a beginning stage
"BS" of subsequent inhalation interval 26 of successive breathing
cycle 28 thereby causing the enhanced opened state of valve
assembly 30. Beginning stage "BS" represents the third
predetermined percentage multiplied by the peak negative pressure
value of the immediate breathing cycle which is used in the
subsequent inhalation interval. In the second opened state of
second solenoid valve V2, the additional treatment gas flows as a
high flow-rate pulse reflected by the spiked solid line portion 72
of flow trace 70. The solenoid valve V2 is operative to actuate
from the second opened state to the second closed state at later
stage "LS" of subsequent inhalation interval 26 of successive
breathing cycle 28. Later stage "LS" represents the second
predetermined percentage multiplied by the negative peak pressure
value of the immediate breathing cycle. Thus, although not by way
of limitation, solenoid valve V1 and solenoid valve V2 actuate to
their respective closed states simultaneously. Preferably, later
stage "LS" occurs before the negative peak pressure value of the
subsequent inhalation interval. Furthermore, solenoid valve V1 and
solenoid valve V2 respectively actuate to the first closed state
and the second closed state when the second predetermined
percentage of negative peak pressure value 36 is achieved. In any
event, treatment gas flows at a flow rate selected from a flow rate
range of 0.5 liters per minute and 12 liters per minute
inclusive.
[0155] In a presently preferred embodiment of a method for
providing a continuous flow of treatment gas to the patient 14 in
the continuous delivery mode is to employ a bypass valve V3
connected between source 12 of the treatment gas, such as
pressurized liquid or gaseous oxygen or ambient air with an
enriched oxygen level or some other gas, and gas delivery tube 52.
Bypass valve V3 diverts flow of the treatment gas around the main
flow control valve, such as solenoid valves V1 and V2 in FIG. 2, so
that the treatment gas is supplied in a continuous flow via the
bypass valve V3 and directly to entrance 16 into the respiratory
system of patient 14, such as at nasal cannula 50.
[0156] When the conserver 6 is in normal operation 140, bypass
valve V3 is in a first operative position which directs the
treatment gas to solenoid valves V1 and V2 for intermittent supply
to the patient 14, as necessary. In system failure mode 152, bypass
valve V3 is energized by conserver 6 to a second operative position
in which bypass valve V3 diverts the treatment gas around solenoid
valves V1 and V2 and to a diversion conduit 156 which is connected
to conduit 52 downstream from solenoid valves V1 and V2, thereby
supplying a continuous flow of the treatment gas directly to
patient. Bypass valve V3 may be implemented, for example, as a
latching valve or some other conventional valve which has two
stable positions and which will preferably automatically move to a
stable open position upon a failure of power to bypass valve
V3.
[0157] In an alternate embodiment, a single combined supply valve
(not shown) can replace both solenoid valves V1 and V2 and the
bypass valve V3. The combined supply valve must, however, have a
normally "open" position that allows the flow of treatment gas
therethrough to the facial interface and a biased "closed" position
which interrupts or prevents the flow of treatment gas through the
combined supply valve. That is, combined supply valve is not
energized or powered during the "on" treatment gas supply cycle.
That is, in the "on" part of the treatment gas supply cycle,
combined supply valve is in its normally open position and
unpowered state wherein the treatment gas is supplied to the
patient. The combined supply valve is in the powered or energized
state only during the "off" part of the treatment gas supply cycle
whereby the combined supply valve is biased into its closed
position where it interrupts or stops the flow of treatment gas to
the patient.
[0158] Therefore, and because of the design and operation of
combined supply valve, combined supply valve will automatically
return to its normally "open" position and will thereby allow the
continuous supply of oxygen to the patient at the pressure and flow
rate determined by the regulator in the event of loss of power or a
malfunction of some other component of the conserver 6.
[0159] Lastly in this regard, it must be noted that the flow of
treatment gas to patient 14 when the conserver 6 is operation in
the system failure mode 152 is controlled by a flow control
regulator 158 located along the treatment gas delivery path and the
treatment gas will be delivered to patient 14 at the pressure and
the flow rate determined by the flow control regulator 158 when
conserver 6 is in system failure mode 152. Depending upon the
specific implementation of the apparatus 10, the patient 14 may, if
necessary or desirable, adjust or alter the flow rate of the
treatment gas by manipulation of the flow control regulator
158.
[0160] Therefore, if the flow control regulator 158 is, for
example, set to deliver oxygen or some other treatment gas at a
flow rate of 5 liters per minute and a pressure of 1 p.s.i., for
example, the combined supply valve (not shown) will remain in its
normally "open" position when conserver 6 is in the system failure
mode 152 and will thereby not interrupt or prevent the continuous
delivery of the treatment gas to the patient 14.
[0161] Since certain changes may be made in the above described
improved conserver and method for conserving oxygen, without
departing from the spirit and scope of the invention herein
involved, it is intended that all of the subject matter of the
above description or shown in the accompanying drawings shall be
interpreted merely as examples illustrating the inventive concept
herein and shall not be construed as limiting the invention.
* * * * *